We present multifrequency VLBI observations of the blazars 3C273 and 3C279 after detecting strong γ-ray flares in both of them. 3C273 exhibited a prominent flare in γ-rays in September 2009 which was followed by a strong flare in the 7 mm VLBI core and emergence of a new feature in the parsec scale jet. We have used time delay between flares in different wavebands together with kinematic analysis to determine that the γ-ray emission zone in 3C273 is located 3.6-5.3 pc upstream from the apparent 7 mm core. We have also analyzed frequency dependent core position to measure a deprojected distance between 7 mm core and the true base of the jet: 1-6 pc for 3C273 and 1-3 pc for 3C279, depending on observing epoch. For 3C279 light curve analysis did not give a robust γ-radio delay because there were too many overlapping flares in this source during considered period.
