A Russian Mi-28N attack helicopter crashed in Syria in the early hours of Tuesday, killing its two pilots, Russian state media reported.
The helicopter, flying a mission in the central province of Homs, was apparently not shot down, Russia's Defence Ministry said in comments carried by state news agency TASS.
The military is trying to discern the cause of the crash, and the two bodies were recovered and brought to a Russian airbase on the Syrian coast, a Defence Ministry spokesman told TASS.
The Interfax news agency cited an undisclosed source in the military as saying that the pilots were wearing night-vision goggles and flying in complete darkness over little-known terrain.
"There could have been some kind of obstacle on the flight path that the helicopter crashed into," the source was quoted as saying.
The crash occurred at 1:29 local time (23:29 GMT) close to the city of Homs, the TASS news agency reported, adding that Mi-28N "Night Hunter" helicopters were being frequently used to secure the nearby city of Palmyra, in the Homs province.
Russian President Vladimir Putin's spokesman told reporters that the cause of the crash was most likely a "technical malfunction," TASS reported.
Russia has been a key ally to Syrian President Bashar al-Assad and launched an airstrike campaign in his support in late September 2015.