Four Russian military personnel were killed, three others wounded in clashes in Syria's Deir el-Zour, Russian defense ministry said Sunday.

According to the ministry statement, the Russian servicemen were killed in a nighttime shelling by several mobile groups of "terrorists."

Two military advisers died on the spot, while two others succumbed to their wounds in a hospital, the statement added.

The Russian military was accompanying the Assad regime forces when clashes erupted. Some 43 "terrorists" were killed in the one-hour fighting.

Russia has conducted a military campaign in Syria since September 2015, helping reverse the course of the war in Bashar Assad's favor.