MOSCOW — The main Russian air and naval bases in Syria beat back an attack by 13 armed drones over the weekend, the Russian Ministry of Defense said on Monday.

The small drones were shot down before they caused any damage and there were no casualties, according to a statement on the military’s Facebook page.

But the attack could indicate that militants opposed to the government of President Bashar al-Assad were stepping up the violence directed against the Russian military, which intervened in September 2015 to prop up the beleaguered Syrian government, then its main ally in the Middle East.

Two Russian military personnel died in a mortar attack against the Hmeimim air base on Dec. 31, the military announced last week.