Two Russian pilots have been killed after their military helicopter was shot down by fighters of so-called Islamic State, the Russian military is quoted as saying by local media.
The Syrian Mi-25 helicopter flown by Riafagat Khabibulin and Yevgeny Dolgin was brought down east of the ancient city of Palmyra on Friday.
It was involved in an anti-IS operation at the Syrian government's request.
IS later claimed responsibility for the attack, the Site monitoring group says.
The helicopter pilots "had received a request from the Syrian military to carry out strikes against advancing militants", the Russian military said in a statement, according to local media.
They "had used up all their ammunition and were on their way back when they came under the fire of terrorists and crashed in an area held by Syrian government troops".
Both pilots have been nominated for Russian state awards.
At least 12 Russian soldiers have been killed since Moscow launched its military operation in Syria in September 2015.
In November, Turkish fighter planes shot down a Russian bomber on the Syrian-Turkish border, triggering a major crisis in bilateral relations.
Russia is helping the Syrian government forces of President Bashar al-Assad against IS and other rebel groups, mainly supporting the Syrian army with air strikes.
The West accuses Russia of also targeting Syria's moderate opposition and civilians - a claim denied by the Kremlin.