Two Russian pilots died near the Syrian city of Palmyra when their helicopter was shot down by Islamic State fighters, bringing the total number of Russian troops killed in the Syrian conflict to 12, Moscow said.
The defence ministry said a Syrian helicopter flown by Riafagat Khabibulin and Yevgeni Dolgin "came under fire" from IS on Saturday and crashed.
The jihadist group claimed responsibility for the attack, according to SITE monitoring group.
The pilots "had used up all their ammunition and were on their way back when they came under the fire of terrorists and crashed," the defence ministry said, adding: "The crew died."
SITE quoted an IS statement as saying: "Soldiers of the Caliphate downed a Russian assault helicopter when it attempted to attack their positions. This resulted in its destruction and killed those who were on board."