Russia's Defense Ministry says a Russian military adviser has been killed by mortar fire in Syria.

The ministry said in a statement that the officer was fatally wounded Monday by mortar shelling from the Islamic State group. Wednesday's statement, carried by Russian news agencies, said the officer was helping train the Syrian military in using Russian weapons. It didn't identify the officer or specify where he died.

The officer's death is the third combat casualty the Russian military has suffered since it launched its air campaign in Syria four months ago.

A Russian pilot whose warplane was downed by a Turkish fighter at the Syrian border was shot dead by militants as he descended by parachute. His crewmate survived, but a Russian marine was killed during the rescue mission.