Subsequent Agreements Regarding Anomalous Categories of ‘Use of Force’: The 1974 Definition of Aggression

It is instructive to examine anomalous acts which States agree fall within the scope of article 2(4). For this purpose, the 1974 Definition of Aggression serves as a key example.Footnote ¹ As explained in Chapter 5, the 1974 Definition is a subsequent agreement on the interpretation of the prohibition of the use of force in article 2(4) of the UN Charter under article 31(3)(a) of the Vienna Convention on the Law of Treaties (VCLT). Some of the acts of aggression (and therefore ‘uses of force’) referred to in the 1974 Definition of Aggression are not strictly ‘armed’ or kinetic forms of force. Article 2 of the 1974 Definition of Aggression provides that:

Article 3 lists acts which may qualify as acts of aggression and is set out and discussed later in the chapter. It provides that: ‘Any of the following acts, regardless of a declaration of war, shall, subject to and in accordance with the provisions of article 2, qualify as an act of aggression’. Article 4 notes that ‘[t]he acts enumerated [in article 3] are not exhaustive and the Security Council may determine that other acts constitute aggression under the provisions of the Charter’. Since articles 1 and 2 of the Definition refer to ‘armed force’, the acts listed in article 3 must all only relate to armed force. As some of the listed acts do not conform to a normal understanding of ‘force’ and do not exhibit all the elements identified in the preceding chapters, it is helpful to examine those acts to assist in the interpretation of the term ‘use of force’ in article 2(4) of the UN Charter. The relevant acts that will be analysed are invasion and military occupation (article 3(a)), blockade (article 3(c)), mere presence in violation of a Status of Forces Agreement (SOFA) (article 3(e)) and indirect use of force either through inter-State assistance (article 3(f)) or through non-State armed groups (article 3(g)).

Lower Gravity Anomalous Examples of ‘Use of Force’

In addition to the acts set out in the 1974 Definition, there are other anomalous examples of acts characterised by States as a prohibited ‘use of force’ despite a lack of certain elements such as ‘use’ of physical force or a lack of physical effects. These include the following:

Forcible Response to Aerial Incursion

The previous analysis discussed State practice regarding aerial incursion into sovereign airspace and its characterisation as a ‘use of force’ in some instances. A related anomaly is the legal characterisation of forcible response to such incursion, such as shooting down the aircraft, as not a ‘use of force’ and therefore falling outside the scope of the jus contra bellum. For instance, in 1983, the Korean aircraft KAL flight 007 was mistaken for a spy plane and shot down by fighters in Soviet airspace. This was widely condemned but article 2(4) was not invoked; instead, the shooting down of the aircraft was condemned as inhumane and disproportionate and in violation of Annex 2 of the Chicago Convention on International Civil Aviation (‘Chicago Convention’) regarding interception of civilian aircraft.Footnote ⁶⁷ In 1996, the Cuban Air Force shooting down two civil aircraft was widely condemned as a violation of article 3bis of the Chicago Convention and resulted in UN Security Council Resolution 1067 (1996) condemning it without mentioning article 2(4) of the UN Charter.Footnote ⁶⁸

Scholars are divided over the question of whether the use of force by a State against intruding military aircraft in its own territory is governed by the jus contra bellum, or law enforcement/air law.Footnote ⁶⁹ For example, Olivier Corten argues that the shooting down of a single military aircraft intruding in airspace is governed by air law rather than the jus contra bellum: ‘if the measures taken against an intruding aircraft are considered police measures for air security, we are referred on to other conditions of lawfulness: prior warning, unless there is a manifest hostile intent, necessary and proportionate measure, or riposte in self-defence’.Footnote ⁷⁰ In Corten’s view, air law and the jus contra bellum have ‘two separate domains of application’.Footnote ⁷¹ In support of this view, he cites articles 1 and 3bis(a) of the Chicago Convention (the latter which however states that ‘[t]his provision shall not be interpreted as modifying in any way the rights and obligations of States set forth in the Charter of the United Nations’). Corten also notes the International Law Commission’s discussion of circumstances precluding wrongfulness uses the example of an aircraft in distress entering airspace unauthorised as being justified as force majeure or distress. Since the ILC regards article 2(4) as a peremptory norm, this aircraft example must not fall under the jus contra bellum but under aviation rules since violations of jus cogens cannot be justified by circumstances precluding wrongfulness and lex specialis is not applicable to such norms.Footnote ⁷² According to Corten, the way to determine which body of rules is applicable depends ‘on the type of action in question, whether a simple police measure in the first instance, or an act of force in international relations in the second’.Footnote ⁷³

In contrast to Corten, Tom Ruys argues:

He concludes that: ‘whenever state A deliberately uses (potentially) lethal force within its own territory – including its territorial sea and its airspace – against military or police units of state B acting in their official capacity, that action by state A amounts to the interstate use of force in the sense of UN Charter Article 2(4).’Footnote ⁷⁵

A more recent incident raising this issue concerned the shooting down of a Russian fighter jet by Turkey on 24 November 2015. The jet was in the region as part of Russia’s ongoing operation in Syria fighting the opposition with the consent of the Assad government. Russia disputes that its jet crossed the Turkish border, but Turkey claimed that:

Russia strongly protested against the shooting down of its jet and claimed that at the time it was shot down, it was 4 km within Syrian territory. It is clear that if Russia’s aerial incursion was an armed attack, Turkey would have the right to use force in self-defence under article 51 of the UN Charter. Under the jus contra bellum, Turkey’s response would be governed by the conditions of necessity and proportionality.Footnote ⁷⁷ If it is proportionate to the goal of halting the attack,Footnote ⁷⁸ then the plane may be shot down. The key issue would then be when the right to self-defence arises – that is, when an ‘armed attack’ ‘occurs’. There are different views regarding when the right to self-defence arises: for example, ‘interceptive self-defence’Footnote ⁷⁹ or imminence.Footnote ⁸⁰ But if such an aerial incursion does not constitute an armed attack, then there is difficulty with explaining the legal basis for response to those small-scale incidents due to the ‘gap’ between a prohibited ‘use of force’ under article 2(4) and the higher gravity threshold of an ‘armed attack’ under article 51.

It remains disputed whether there is a right to use force against intruding military aircraft unless in self-defence.Footnote ⁸¹ But since it is very restrictive to hold that States can only respond to aerial incursions by military aircraft within their territory with force in the event of a strictly construed armed attack, there are three legal possibilities to address this. Firstly, one can interpret a lower threshold for ‘armed attack’ giving rise to a right of self-defence. Secondly, one can find an exception to the prohibition of the use of force outside article 51 self-defence and Chapter VII enforcement action – for example, ‘proportionate defensive action against incipient attack’,Footnote ⁸² or forcible countermeasures by the victim State to acts violating article 2(4) but falling short of article 51 armed attackFootnote ⁸³ (however, this view is firmly in the minority position since it is widely accepted that since the advent of the UN Charter, forcible countermeasures, that is armed reprisals,Footnote ⁸⁴ are unlawful).Footnote ⁸⁵ The third possibility – which would constitute an anomalous example of non-use of force – is to interpret the prohibition of the use of force as not applying to a State’s use of force against incursions by the military of another State within its own territory. This could either be on the basis that the contextual requirements of article 2(4) are not met, since the forcible act is not ‘in international relations’ or against the territorial integrity or sovereignty of another State or against the purposes of the United Nations, or on the basis that the act does not constitute a ‘use of force’.

Maritime Law Enforcement against Foreign-Flagged Vessels with No Basis for Jurisdiction

A further example of forcible acts that appear to meet the criteria for a ‘use of force’ but are not consistently characterised as such relates to maritime law enforcement against foreign-flagged vessels that is without lawful basis. The use of force at sea is a complex issue, because it is governed by a parallel legal regime: the law of the sea. The law of the sea as embodied in the UN Convention on the Law of the Sea (UNCLOS)Footnote ⁸⁶ recognises different legal spaces at sea and strikes a balance between the rights of coastal States and the general interest of all States to freedom of navigation and peaceful uses of the sea. The resulting regime can result in multiple States having enforcement jurisdiction over the same physical space because of the principle of exclusive flag State jurisdiction, territorial sovereignty of the coastal State over internal waters and the territorial sea (with the territorial sea subject to certain rights of other States such as innocent passage), a customs and immigration enforcement area within the contiguous zone but outside territorial waters, and the exclusive economic rights of the coastal State within its Exclusive Economic Zone (subject to freedoms of the high seas such as navigation, overflight and laying of cables). This is the most fraught zone of the seas, because it is here that there is a complex balance between the rights of the coastal State and the rights of all other States; this is a result of a compromise to create a new zone, the Exclusive Economic Zone of 200 nautical miles, while preserving other rights of third States. Not all rights are assigned within this area, so there remains uncertainty over the legal rights that the coastal State and other States are entitled to exercise within this zone. UNCLOS also recognises other maritime spaces such as transit straits, archipelagic seas and the high seas (subject to freedom of navigation and peaceful uses).Footnote ⁸⁷

In respect of purported maritime law enforcement with no basis for jurisdiction, despite the presence of elements of a ‘use of force’ identified in Part II, States do not always characterise such acts as a violation of article 2(4) of the UN Charter. The following section will discuss two examples of anomalous non-uses of force: response to non-innocent passage through the territorial sea by submerged submarines and unlawful attempts to exercise law enforcement jurisdiction on the high seas against foreign vessels (which has no legal basis outside certain recognised exceptions under customary international law and treaty, e.g. article 110 of UNCLOS).

An anomalous example of forcible acts which are not usually characterised as an unlawful ‘use of force’ is the forcible response to non-innocent passage of submerged submarines through the territorial waters of another State. The coastal State has sovereignty over the territorial sea, which may extend twelve nautical miles from the baseline.Footnote ⁸⁸ Foreign vessels, including warships and submarines, have a right of innocent passage through the territorial sea.Footnote ⁸⁹ According to article 19(1) of UNCLOS, ‘[p]assage is innocent so long as it is not prejudicial to the peace, good order or security of the coastal State. Such passage shall take place in conformity with this Convention and with other rules of international law’. Article 19(2) of UNCLOS specifies acts which render passage not innocent, including ‘(a): any threat or use of force against the sovereignty, territorial integrity or political independence of the coastal State, or in any other manner in violation of the principles of international law embodied in the Charter of the United Nations’. Article 20 states that: ‘[i]n the territorial sea, submarines and other underwater vehicles are required to navigate on the surface and to show their flag’. Furthermore, according to article 25(1): ‘[t]he coastal State may take the necessary steps in its territorial sea to prevent passage which is not innocent’. Under customary international law, foreign government vessels such as warships and submarines have sovereign immunity from the jurisdiction of any State except their flag State.Footnote ⁹⁰ UNCLOS is silent on the measures that may be taken in response to non-innocent passage, and its article 25 does not explicitly authorise a forcible response to non-innocent passage. Thus, it is unclear which legal regime governs the forcible response of the coastal State to non-innocent passage by foreign government vessels.

This issue comes to the fore in instances of submerged submarines entering the territorial waters of another State in violation of article 20 of UNCLOS. For example, in 1982,

A similar issue was raised in 2004 when a submerged submarine which was later identified as Chinese entered Japan’s territorial sea. ‘[A] “maritime security operation” (kaijo-keibi-kodo) was ordered to the Commander of the Japan Maritime Self-Defense Force (JMSDF) Fleet, and patrol helicopters and vessels of the JMSDF joined the operation.’Footnote ⁹² The incident was framed by Japan as a violation of international law (specifically of article 20 of UNCLOS to which Japan and China are party). There was no invocation of the language of article 2(4) or article 51 of the UN Charter. Japan demanded an apology, explanation and assurance of non-repetition. Despite calls in the Japanese Diet for greater clarity over the measures that may be taken against submerged submarines in such situations, the government response plan does not address what measures it believes a State may take in response to violations of article 20.Footnote ⁹³

These examples are anomalous because a coastal State may not exercise law enforcement jurisdiction over a foreign warship or submarine, since foreign government vessels enjoy sovereign immunity. Thus, a use of force against submerged submarines in the territorial sea in an attempt to bring them to the surface and require them to leave the territorial sea is not authorised by UNCLOS nor customary international law. ‘To the extent that any maritime security threats or breaches are state sponsored, law enforcement powers against sovereign immune vessels are not available. Instead, questions involving the threat or use of force may arise and diplomatic or other avenues for dispute settlement must be pursued.’Footnote ⁹⁴ In the absence of a basis for the exercise of jurisdiction against such vessels, a use of force against them would appear to be in international relations and fall within the ambit of the prohibition of the use of force under article 2(4) of the UN Charter, so it is curious that States do not always invoke self-defence to respond to submerged submarines in territorial waters. However, omitting to invoke article 2(4) or article 51 does not necessarily indicate an opinio juris that such incidents definitively fall outside the scope of article 2(4), since it could be motivated by other considerations (such as political) and also due to uncertainty over the applicable legal framework.

With respect to attempted law enforcement against foreign-flagged vessels on the high seas, this is sometimes but not always characterised as an unlawful use of force under the jus contra bellum. On the high seas, the principle of mare liberum and exclusive flag State jurisdiction with only few exceptions applies. This was affirmed by the Permanent Court of International Justice in the SS Lotus case: ‘It is certainly true that – apart from certain special cases which are defined by international law – vessels on the high seas are subject to no authority except that of the State whose flag they fly.’Footnote ⁹⁵ Exceptions to sole flag State jurisdiction on the high seas include the right of hot pursuit, plus ‘the right of visit in relation to piracy, slave trading, drug trafficking, people smuggling, and unauthorized broadcasting’.Footnote ⁹⁶ Therefore, attempts by a State to exercise jurisdiction against a foreign vessel on the high seas outside of these recognised exceptions or on the basis of a specific treaty (such as the 1995 Fish Stocks AgreementFootnote ⁹⁷) have no legal basis. With respect to interdiction (unilateral boarding and arrest of a vessel) by the non-flag State on the high seas, Douglas Guilfoyle argues that such unauthorised interference is ‘a clear attack on a State’s sole means of exercising a fundamental right’.Footnote ⁹⁸

A prominent example of high-gravity employment of force in purported law enforcement on the high seas without lawful basis is the 1967 bombing of a Liberian-flagged oil tanker, Torrey Canyon, by the United Kingdom to prevent marine pollution after it ran aground on the high seas outside British territorial waters.Footnote ⁹⁹ ‘The operation, conducted by the RAF, lasted several days with napalm bombs being dropped on the wreck to release and burn the oil remaining in the ship’s tanks.’Footnote ¹⁰⁰ The legal debate following the incident turned around the lawfulness of police measures on the high seas to prevent the risk of pollution, including the possibility of invoking necessity as a ground precluding wrongfulness.Footnote ¹⁰¹ Although the UK had no grounds for exercising law enforcement jurisdiction over the Liberian-flagged vessel on the high seas, and despite the high gravity of means and physical effects, the incident was not characterised as a ‘use of force’ under article 2(4) of the UN Charter. Corten argues that this precedent confirms that two separate legal frameworks can apply to the use of force at sea: one relating to police measures based on treaty or customary rules of the law of the sea, and the other governed by the jus contra bellum.Footnote ¹⁰² However, due to the lack of legal grounds for exercising law enforcement jurisdiction in this case, this argument is not convincing and the reasoning may lie elsewhere.Footnote ¹⁰³

The Fisheries Jurisdiction (Spain v Canada) caseFootnote ¹⁰⁴ before the ICJ is also sometimes cited in support of the argument that there is a de minimis gravity threshold that divides a ‘“minimum use of force”, that can be ascribed to simple police measures, and a more serious use, that might come within the ambit of article 2(4)’.Footnote ¹⁰⁵ In this case, Canada had entered a reservation to its acceptance of the Court’s compulsory jurisdiction excluding the Court’s jurisdiction over ‘disputes arising out of or concerning conservation and management measures taken by Canada with respect to vessels fishing in the NAFO Regulatory Area, as defined in the Convention on Future Multilateral Co-operation in the Northwest Atlantic Fisheries, 1978, and the enforcement of such measures’. On the same day, Canada introduced domestic legislation regarding conservation and management measures over parts of the high seas. Canada then later enforced that legislation on the high seas 245 miles from the Canadian coast against a Spanish fishing vessel, the Estai, by boarding, inspecting and seizing the vessel. Spain protested and claimed that this was an unlawful use of force in violation of article 2(4). Canada argued that the Court had no jurisdiction to hear the dispute, since it fell within the scope of its reservation. Spain argued that since the acts complained of were unlawful under the UN Charter, they could not be regarded as falling within the scope of the Canadian reservation. Consequently, the case ultimately concerned whether the matter was a ‘dispute[] arising out of or concerning conservation and management measures taken by Canada with respect to vessels fishing in the NAFO Regulatory Area, as defined in the Convention on Future Multilateral Co-operation in the Northwest Atlantic Fisheries, 1978, and the enforcement of such measures’.

The Court found that it had no jurisdiction because the measures taken against the Estai fell within the scope of Canada’s reservation. In particular, it stated:

This statement has been relied upon by Corten to support his position regarding a de minimis gravity threshold distinguishing law enforcement measures from a ‘use of force’ at sea. However, a close reading of the judgment shows that the Court was not drawing a boundary between ‘use of force’ under article 2(4) and the enforcement of conservation and management measures at sea. In fact, the Court explicitly declined to scrutinise the legality of the measures under international law (including article 2(4) of the UN Charter) since it did not have jurisdiction to do so.Footnote ¹⁰⁷ The Court confined itself to interpreting ‘conservation and management measures’ in a technical sense (to see if the acts fell within the scope of Canada’s reservation from its acceptance of the Court’s jurisdiction) and was careful to distinguish this from the legality of the measures under international law. It was therefore left unsettled whether the enforcement measures violated article 2(4). This case therefore provides no support either in favour or against a gravity threshold that distinguishes law enforcement measures and a ‘use of force’ under article 2(4).

Conclusion

An analysis of anomalous examples of non-‘use of force’ such as forcible response to aerial and maritime incursion and purported maritime law enforcement may further clarify the complex relationship between competing applicable legal frameworks and where the boundaries between them lie, as well as indicate which elements of a ‘use of force’ are necessary and the relationship between those elements. The next section will discuss possible legal explanations for these anomalous ‘uses of force’ and non-‘uses of force’ under article 2(4) of the UN Charter.

1. These Are Agreed Exceptions to the General Interpretation of Article 2(4)

One possibility is that these anomalous examples are merely agreed exceptions to the general interpretation of a ‘use of force’ under article 2(4) and customary international law. This possibility is not excluded but would need to be strongly supported by subsequent agreement or evidence of subsequent practice demonstrating the parties’ agreement to this interpretation. If one considers 1974 GA Resolution 3314 as a subsequent agreement regarding the interpretation of article 2(4) of the UN Charter,Footnote ¹⁰⁸ an argument could be constructed to support recognised exceptions to the general interpretation of this term, as set out in the preceding section, namely: military occupation (as distinct from the invasion or armed attack preceding it) (article 3(a)), an unenforced blockade (article 3(c)), mere continuing presence in contravention of SOFA (article 3(e)) and indirect aggression either through ‘[t]he action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State’ (article 3(f)) or ‘[t]he sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts listed above, or its substantial involvement therein’ (article 3(g)). In this case, the general definition of a prohibited ‘use of force’ would apply, requiring the presence of the identified elements of a ‘use of force’, unless an act fell within the scope of an agreed special case.

This is of course possible, but there are two issues with this explanation. The first is that it would be preferable to find a solution that results in a consistent interpretation of this provision. This is not an insurmountable objection, since it may be that this is the situation lex lata even though it may not be the preferred interpretive outcome as a matter of legal policy. The second and more important issue with this explanation is that, although it explains certain anomalous examples of ‘use of force’ that do not display the usual elements (such as physical means or physical effects), it does not fully explain the phenomena in question. For instance, it does not explain anomalous examples of non-use of force discussed earlier (although of course, these could also be subsequent agreements regarding acts that fall outside the scope of the prohibition). It also does not provide a satisfactory definition of an unlawful ‘use of force’ for acts that do not fall within subsequently agreed special exceptions to the general definition. As will be argued in more detail in the following chapter, a prohibited ‘use of force’ (even one that is a ‘standard’ type of force and not a special case such as unresisted invasion) is not characterised by a checklist of essential elements. The theory of subsequently agreed special types of ‘use of force’ therefore does not provide a full explanation of how to identify whether certain acts fall within the general definition.

2. The Interpretation of ‘Use of Force’ Is Broader than Generally Understood

An alternative explanation for these anomalous uses of force and non-uses of force is that the definition of a prohibited ‘use of force’ is broader than previously understood and encompasses acts which do not conform with the typical understanding of ‘force’ as derived in Part II. The 1974 Definition of Aggression could be regarded as a subsequent agreement that shows that UN Member States share a broader understanding of the concept of ‘armed force’. The majority of the acts listed (articles 3(a)–(d)) involve classical acts of inter-State warfare, namely, invasion, military occupation, bombardment, blockade and attacks on the armed forces of a State or its marine and air fleets. The remainder of listed acts involve a special case of violation of sovereignty that could be (at a broad level) considered similar to military occupation due to the unconsented to and thus unlawful presence of the armed forces of another State within a State’s territory (in the case of article 3(e)), and as closing loopholes in unlawful conduct by enclosing forms of indirect aggression such as certain forms of assistance to another State to commit aggression (article 3(f)) or through sending/substantial involvement in the armed attack against a State by a non-State armed group (article 3(g)). All of these acts (including the case of attacks against the marine or air fleets of a State, due to the nexus to the State demanded by the scale of the attack, as denoted by the term ‘fleets’) share in common a violation of the territorial integrity, sovereignty and political independence of the victim State and serve to protect these interests. Therefore, in this sense it could be hypothesised that an unlawful use of force is something broader than the application of violence between States and encompasses any significant injury to the fundamental rights of State sovereignty and political independence.

This is more satisfactory than the previous hypothesis, because it provides a coherent (if presently vague) definition of a ‘use of force’. But it is also problematic because like the first hypothesis, it does not fully explain why some acts fall within or outside the definition. Why is it that these acts should still be considered a ‘use of force’ under article 2(4) despite lacking certain elements, such as physical means or physical effects? Does it mean that those elements are not really necessary for an act to constitute a prohibited ‘use of force’? How is this to be reconciled with the fact that most uses of force do display these elements? And, even more problematically, the possibility under consideration does not explain why other acts which may very well violate the territorial integrity, sovereignty and political independence of the victim State are not characterised as prohibited ‘uses of force’, such as certain forms of support for armed non-State groups. To conclude that the anomalous examples discussed earlier are explained by a broader understanding of ‘use of force’ is also unsatisfactory because it risks giving the prohibition of the use of force an overreach.

3. ‘Use of Force’ as a Type Rather than a Concept

The third and arguably more convincing hypothesis is that these anomalous examples of use of force and non-use of force may be reconciled with a consistent interpretation of ‘use of force’ if it is accepted that a ‘use of force’ under article 2(4) of the UN Charter is a type rather than a concept. In other words, it may be that not all of the elements identified in Part II are necessary, although in particular combinations they may be sufficient, to constitute a ‘use of force’. This hypothesis is explored in more detail in Chapter 8.

1. Military Incursion without Recourse to the Use of Weapons

2. Unconsented Presence in Territory

3. Special Case: Indirect Use of Force

Potential Effects, Object/Target and Intention

A use of force with only potential but unrealised effects may require a higher level of (potential) gravity, intention, or an object/target that has a particularly close connection to another State (such as Foreign Minister/President) in order to be characterised as unlawful under article 2(4) of the UN Charter. Although these elements are elements of a ‘use of force’, they may also relate to the contextual element of whether the act is in ‘international relations’. This is illustrated through the juxtaposition of States’ legal characterisation of two attempted killings: that of former US President George Bush in 1993 and of the former Russian intelligence officer Sergei Skripal in England in 2018.

In the first incident, the Iraqi Intelligence Service (IIS) allegedly directed and carried out an attempted assassination of former US President George Bush by planning to explode a car bomb next to his motorcade on a visit to Kuwait from 14 to 16 April 1993.Footnote ²¹ In response, from 26 to 27 June 1993, the United States retaliated by launching twenty-three Tomahawk missiles against the headquarters of the IIS in Baghdad, destroying the building, killing at least six civilians and injuring twenty others. To justify the strike, the United States referred to article 51 of the UN Charter and stated that it was exercising the ‘right to self-defence by responding to the Government of Iraq’s unlawful attempt to murder the former Chief Executive of the United States Government, President George Bush’.Footnote ²² The international response to the US action was mixed.Footnote ²³ However, some States that expressed support or understanding for the US action referred expressly to the nature of the target of the assassination attempt, including Japan, Brazil, New Zealand and Spain.Footnote ²⁴ In particular, New Zealand asserted that ‘any nation that seeks to assassinate the Head of State or a member of the senior political leadership of another State commits an act of aggression. Such actions are at the most serious end of the scale because Heads of State symbolize the sovereignty and integrity of their country’.Footnote ²⁵ Some scholars also ‘emphasized that the protection of a state’s elected officials would be an essential attribute of state sovereignty, especially taking into account the destabilizing effects that an assassination of a Head of State could have on the nation’.Footnote ²⁶ Thus, although the international response to the incident was ‘not unanimous and in most cases not unequivocal’Footnote ²⁷ regarding the US self-defence claim, what matters for our purposes is the characterisation of the attempted killing itself as an unlawful use of force on the basis of the close nexus between the target and the victim State even though the intended harmful effect did not materialise.

In contrast, the attempted killing of Sergei Skripal in the UK by suspected Russian agents shows that when there is a relatively low nexus with the territorial State, the attempted killing of an individual by foreign State agents is not enough on its own for States to widely characterise the incident as an unlawful ‘use of force’ in violation of article 2(4). Mr Skripal (apparently a dual Russian/UK national and former double agent)Footnote ²⁸ and his daughter Yulia were found unconscious on a bench in Salisbury and later hospitalised in serious condition together with an attending police officer. The United Kingdom alleged that a military-grade Novichok nerve agent of a type developed by Russia was used in the attack and accused Russia of being responsible for carrying out the attack. The Russian government denied any involvement.Footnote ²⁹ Despite the use of a chemical weapon allegedly by Russian agents on the territory of the United Kingdom, the attempted killing was not widely denounced as a violation of article 2(4), possibly because of the lack of a particularly close connection between Mr Skripal and the territorial State. For such targets that do not have a close association with a State, other elements of a ‘use of force’ must be more serious to bring the act within the scope of article 2(4), such as the gravity of the (potential) effects, a pre-existing dispute between States or a coercive or hostile intent against a State. In this case, the UK emphasised the gravity of the potential effects of the chemical weapon on the wider public when claiming that the attack on Mr Skripal was an unlawful use of force in violation of article 2(4).Footnote ³⁰ This incident is analysed in more detail as a case study to illustrate the application of type theory later in this chapter.

‘International Relations’, Gravity and Intention

As argued in Chapter 6, the elements of ‘international relations’, gravity and intention are interrelated. This is illustrated in the following case study on excessive or unlawful maritime law enforcement and ‘use of force’. With respect to excessive maritime law enforcement, there is mixed practice in this regard. First of all, why would a use of force against a civilian vessel registered to another State be considered ‘force’ under article 2(4) at all? The reason is the principle of exclusive flag State jurisdiction – a use of force against a civilian vessel by a non-flag State is the exercise of enforcement jurisdiction within a domain subject to the exclusive jurisdiction of another State. It may therefore under certain circumstances fall under ‘international relations’ and be considered to be against the sovereignty of another State (i.e. the flag State). It is important to note that different international law principles apply to use of force in law enforcement versus a use of inter-State force under the jus contra bellum.Footnote ³¹ Patricia Jiminez Kwast makes the important point that there are two separate issues: which legal category applies (law enforcement or use of force), and whether the act complies with the lawful requirements of that category – just because law enforcement action is unlawful under that framework does not automatically render it a violation of the prohibition of the use of force.Footnote ³² Tom Ruys posits that

In light of the increasing constabulary role of navies, especially in the South and East China Seas, the distinction between these two applicable legal frameworks and their boundary is of particular relevance.Footnote ³⁴

State practice shows that States do sometimes consider purported maritime law enforcement to be a use of force. There are numerous examples in State practice where forcible acts at sea were characterised by States as a violation of article 2(4): the 1975 Mayaguez incident (self-defence); the Germany/Iceland Fisheries Jurisdiction case (Germany claimed a violation of article 2(4), although the Court did not rule on this point); the Canada/Spain Fisheries Jurisdiction case (Spain claimed a violation of article 2(4), but the Court held it had no jurisdiction – discussed in Chapter 7); and the Guyana/Suriname arbitration. However, State practice is not consistent and numerous similar incidents have not been characterised as an unlawful use of force under article 2(4). These include the 1962 Red Crusader (Denmark/UK) case, the 1967 Torrey Canyon incident, the 1985 Rainbow Warrior incident and the 1997 M/V Saiga (No. 2) incident. It is therefore instructive to examine these incidents through the lens of type theory (i.e. the identification and balancing of the elements of a ‘use of force’) to see why only some of these incidents were characterised as an unlawful ‘use of force’.

Excessive Maritime Law Enforcement

The Mayaguez incident in 1975 occurred in the context of the Vietnam War and the recent ousting of the US-backed Khmer Republic by the Khmer Rouge. The US-flagged container ship the Mayaguez and its crew were seized by Cambodian naval forces within Cambodian territorial waters, although the United States disputed the twelve nautical mile rule at the time. During the seizure of the vessel, the Khmer Rouge naval vessel fired a machine gun and then a rocket-propelled grenade across the bow of the ship before boarding and seizing the vessel.Footnote ³⁵ The United States launched a rescue operation, citing article 51 of the UN Charter.Footnote ³⁶ The seizure of the Mayaguez was thus considered an unlawful ‘use of force’ (and ‘armed attack’) by the United States, giving rise to a right to self-defence. In this incident, the target of the use of force had a strong connection to the victim State (given the political context) and due to the surrounding events, the forcible act evinced a hostile intent and was clearly in the ‘international relations’ between the two States concerned. Thus, the contextual elements of an unlawful ‘use of force’ were present. In terms of elements of ‘use of force’, the gravity of the physical means was moderate, as was the gravity of the physical effects (the seizure of the vessel and its crew).

In contrast, in the Red Crusader incident in 1962, maritime law enforcement was found to be excessive and unlawful but was not characterised as a violation of article 2(4) of the UN Charter. In that incident, Danish authorities arrested a British-flagged vessel in Danish territorial waters and fired shots at the vessel without warning. The International Commission of Inquiry found:Footnote ³⁷

Similarly, in the 1997 M/V Saiga (No. 2) incident, maritime law enforcement was found to be excessive but not an unlawful ‘use of force’ under article 2(4) of the UN Charter. In that incident, Guinea arrested a vessel flagged to St Vincent and the Grenadines within the Exclusive Economic Zone of Guinea, injuring at least two crew members. St Vincent and the Grenadines did not claim that it was a violation of article 2(4) but of the UN Convention on the Law of the SeaFootnote ³⁹ (UNCLOS) articles 56(2) and 58, 111, 292 (freedom of navigation, violation of hot pursuit conditions and prompt release). The International Tribunal for the Law of the Sea also did not raise article 301 of UNCLOS nor article 2(4) of the UN Charter. The Tribunal instead applied the requirements for lawfulness of use of force in law enforcement measures:Footnote ⁴⁰

In the Red Crusader and M/V Saiga (No. 2) incidents, it is not apparent that the vessels were targeted due to their nationality nor in the context of a political dispute between the States concerned. There was no apparent coercive or hostile intent against the flag State, given that Denmark and Guinea respectively were enforcing domestic laws within their own territorial sea (in the case of the Red Crusader) or Exclusive Economic Zone (in the case of the M/V Saiga (No. 2). As the forcible act did not occur in the international relations between the States concerned, the contextual elements of an unlawful ‘use of force’ are missing. In terms of elements of ‘use of force’, the physical means employed and their physical effects were of relatively low gravity. This coupled with a low nexus and a lack of hostile intent against another State results in an insufficient combination of elements of a ‘use of force’ including their relative weight. Accordingly, these two incidents were deemed to fall within the realm of law enforcement rather than the jus contra bellum.

Maritime Law Enforcement with No Basis for Jurisdiction

In contrast to the previous incidents which involved excessive maritime law enforcement, the following category of incidents involved the purported exercise of law enforcement against foreign-flagged vessels with no (or a disputed) basis for jurisdiction because it took place in the territorial waters of another State, on the high seas or in a disputed maritime zone.

In the incidents of the Fisheries Jurisdiction case (Germany v Iceland) and the Guyana v Suriname arbitration, the purported maritime law enforcement by Iceland and Suriname respectively were characterised by the ‘victim’ State as either an unlawful use or threat of force. These incidents both occurred in disputed maritime zones. In the former case, Iceland sought to unilaterally extend its fisheries jurisdiction to fifty miles from the baseline. Germany challenged this and claimed that Iceland’s actions in enforcing this extended fisheries jurisdiction zone against German fishing vessels by cutting their nets and firing warning shots and live rounds was a violation of article 2(4) of the UN Charter.Footnote ⁴¹ The International Court of Justice (ICJ) did not analyse Germany’s submission regarding use of force in substance. Instead, it made a finding on procedural grounds that it was unable to accede to the submission, since it was not put in concrete terms seeking specific damages with evidence to support each claim.Footnote ⁴² In the case of Guyana v Suriname in 2007, Guyana claimed that the Surinamese navy had violated article 2(4) of the UN Charter by ordering an oil rig and drill ship operating under licences issued by Guyana to leave the disputed maritime zone in which they were operating.Footnote ⁴³ The tribunal held that ‘the action mounted by Suriname on 3 June 2000 seemed akin to a threat of military action rather than a mere law enforcement activity’.Footnote ⁴⁴

Applying type theory to these incidents, they were each characterised by the other State (and by the arbitral tribunal in Guyana v Suriname) as a use or threat of force despite the relatively low gravity of each incident in terms of their physical means and effects. One explanation is that since each incident took place within a disputed maritime zone and as a means of enforcing the State’s claim to that zone, it was a coercive measure in the ‘international relations’ between the respective States. Thus, even incidents of low gravity in physical means and physical effects may suffice to meet the definition of unlawful use or threat of force when combined with a clear coercive intent and when the incident clearly takes place within ‘international relations’.

In contrast, the incident of the Torrey Canyon in 1967, in which the British RAF dropped napalm bombs on a Liberian-flagged oil tanker which ran aground on the high seas (discussed in the Chapter 7), was not characterised as an unlawful ‘use of force’ despite the lack of legal grounds for the UK to exercise law enforcement jurisdiction against the vessel to prevent marine pollution under either treaty or customary international law. Clearly, a high gravity of physical means and physical effects were present in this case. One basis for the lack of any invocation of article 2(4) in relation to this incident could be that the contextual requirement of ‘international relations’ was missing. Given that the UK had a clear and limited intention to release and burn the remaining oil in the vessel’s tanks to prevent marine pollution on the high seas (an intention that was accepted as legitimate by the international community as a whole, as demonstrated by the subsequent adoption of the International Convention on Intervention on the High Seas in Cases of Oil Pollution CasualtiesFootnote ⁴⁵ to permit this type of action), and the application of force, though deliberate, was not coercive or hostile with respect to the flag State, it was not regarded by any State to engage the ‘international relations’ between the UK and the flag State of the vessel, Liberia, or any other State.Footnote ⁴⁶

In the Rainbow Warrior affair, on 10 July 1985, on official orders, French secret service agents carried out an attack against a British-flagged civilian (Greenpeace) vessel moored in the internal waters of New Zealand. Two high explosive devices detonated and sunk the vessel, killing a Dutch citizen who was on board.Footnote ⁴⁷ The New Zealand government argued that the attack against the Rainbow Warrior was a ‘serious violation of basic norms of international law … specifically, it involved a serious violation of New Zealand sovereignty and of the Charter of the United Nations’ and sought reparations.Footnote ⁴⁸ However, New Zealand did not allege a violation of article 2(4). Olivier Corten argues that this is probably because the operation was limited in scope and was not ordered by ‘the highest echelons of the State’.Footnote ⁴⁹ Applying type theory analysis to this incident, we can see that the attack clearly took place in the ‘international relations’ between the two States since it was officially ordered and carried out by French government agents and constituted a serious violation of the sovereignty of New Zealand. However, there was no hostile or coercive intention vis-a-vis New Zealand and although the physical means employed were of relatively high gravity, the physical effect on the ‘victim’ State (New Zealand) was confined to a violation of sovereignty, since the vessel was British-flagged and the person killed in the attack was of Dutch nationality. As such, New Zealand did not treat the matter as an unlawful ‘use of force’ against it but as a domestic crime (by the secret service agents who carried out the attack) and a violation of its sovereignty by France.

This conclusion has implications for a wider debate under jus in bello regarding whether ‘non-consensual force against a non-State actor on the territory of another State is always an [International Armed Conflict (IAC)], as opposed to those who say it is only sometimes an IAC, depending on the circumstances’.Footnote ⁵⁰ The classification of conflict under jus in bello is a separate question to whether an act is a prohibited ‘use of force’ under jus contra bellum and is relevant to whether (and which) rules of international humanitarian law (IHL) apply to the conduct of hostilities. The International Committee of the Red Cross (ICRC) appears to take the first position set out earlier, stating that an IAC ‘arises between the territorial State and the intervening State when force is used on the former’s territory without its consent’.Footnote ⁵¹ The benefit of this approach is that it provides legal certainty regarding the classification of conflict and applicability of IHL rules to ensure protection. Others such as Noam Lubell point out the absurdity of applying this approach to incidents such as the sinking of the Rainbow Warrior since this would lead to the conclusion that there was an IAC between France and New Zealand, which ‘would … seem incongruous with the notion of IAC’ and lead to inappropriate application of IHL rules to the situation.Footnote ⁵² The conclusion of the type theory analysis in this chapter that the sinking of the Rainbow Warrior was not a ‘use of force’ under article 2(4) of the UN Charter allows a way out of the impasse and has the potential to provide clarity to the debate on classification of conflict under jus in bello when States use force against non-State actors on the territory of another State. A more detailed analysis of the relationship between ‘use of force’ under jus contra bellum and classification of conflict under jus in bello is beyond the scope of this book.