(Reuters) The Russian air force grounded its entire fleet of Sukhoi-27 fighter jets on Thursday after a fatal crash near Moscow which aviation sources told Russian agencies looked like the result of some kind of technical failure.

Viktor Bondarev, the head of the air force, ordered the country’s fleet of the twin-engined fighter jet grounded until the reasons for the crash had been determined, Russian agencies reported.

Russia is believed to have over 300 of the fighter jets in service. The United States complained in April that one of them had made aggressive maneuvers near a U.S. reconnaissance plane over the Baltic Sea, a charge Russia rejected.

Thursday’s crash occurred just outside Moscow and involved an SU-27 that was part of the country’s famous aerobatic demonstration team, the ‘Russian Knights,’ who have overflown annual Red Square military parades in the past.

The Russian Defence Ministry was quoted as saying that the pilot of the downed plane, who was killed, did not have time to eject because he had used his last seconds to steer the aircraft away from a populated area.

The plane was returning to its base at the time and was not carrying weapons or ammunition, the ministry was cited as saying. A Defence Ministry commission is reported to be working at the crash site to try to determine what happened.

Release Reuters