Russia's Defense Ministry says two of its soldiers were killed in a mortar attack on the Russian air base in Syria.

The ministry says the attack on the Hemeimeem base took place on Sunday and that it was carried out by a "mobile sabotage group" of fighters.

Thursday's reports by the state news agencies Tass and RIA-Novosti did not specify the attackers' affiliation or say if they were members of a specific rebel or militant group in Syria.

Russian forces also lost a helicopter in a Sunday crash in Syria that killed one of the two pilots. The ministry said a technical fault caused the crash and that the Mi-24 did not come under fire.