A Russian Mi-28N Night Hunter attack helicopter crashed in Syria in the early hours of Tuesday morning killing both pilots, Russia's Defence Ministry said.
The ministry said the helicopter, which crashed in Homs province, had not been shot down, but the cause of the incident was unclear.
"A group of specialists is working at the crash site to investigate the incident," the ministry said in a statement. The pilots' bodies had been recovered and brought back to Russia's air base in Hmeymim in Latakia province, it said.
President Vladimir Putin announced on March 14 that Russia was withdrawing the bulk of its military contingent in Syria. Around half its fixed-wing strike aircraft flew out in the days that followed.
But Russia continued to ship significant quantities of military supplies to Syria and analysts said the Kremlin had changed rather than diluted its military capabilities, increasingly relying on helicopters to support the Syrian army.
Mi-28N helicopters, broadly equivalent to America's Apache gunship, took part in the Syrian government operation to push Islamic State out of the ancient city of Palmyra last month, firing anti-tank rockets at armoured vehicles.