The covert Russian attempts of overthrowing Dudayev by means of armed Chechen opposition forces resulted in repeated failed assaults on the city. Originally, Moscow had been backing the political opposition of Umar Avturkhanov "peacefully" (i.e. without supplying the opposition with weapons and encouraging them to try a coup). However, this changed in 1994, after the coups in neighboring Georgia and Azerbaijan (both of which Moscow was involved with), and Russia encouraged armed opposition and occasionally assisted. In August 1994 Avturkhanov attacked Grozny, but was repelled first by Chechen citizens who were then joined by Grozny government troops and Russian helicopters covered his retreat. On September 28, one of these interfering helicopters was shot down and its Russian pilot was held as a prisoner-of-war by the Chechen government. The last one on 26 November 1994 ended with capture of 21 Russian Army tank crew members, secretly hired as mercenaries by the FSK (former KGB, soon renamed FSB); their capture was sometimes cited as one of the reasons of Boris Yeltsin's decision to launch the open intervention. In the meantime, Grozny airport and other targets were bombed by unmarked Russian aircraft.