Russia's Defence Ministry said that one of its top generals Valery Asapov has been killed by mortar shelling in Syria.
The attack on a Syrian military outpost was carried out by ISIS fighters near the war-torn city of Deir al-Zor.
The ministry said Asapov died at a command station manned by Syrian troops, assisting commanders in the liberation of the city.
"As a result of a sudden mortar shelling by ISIS militants, Lieutenant-General Valery Asapov was fatally wounded by an exploding shell,” the ministry said.
Asapov was one of the senior Russian military advisers working on the ground in Syria.
In recognition of his services, Lieutenant-General Asapov is to be presented with a posthumous state decoration, the SUN reported.