Russia is calling for "concrete action" after a shell landed on its embassy compound in the Syrian capital, Damascus.
The Foreign Ministry said on September 21 that the mortar attack was launched in the morning of September 20 by forces battling Syrian President Bashar al-Assad.
It said the shelling did not cause damage.
The militants have "outside sponsors" who are responsible for influencing their actions, the ministry said.
"We are expecting a clear-cut position on this act of terror from all members of the international community,” it added. “What is needed is not just words but concrete action too."
The statement comes amid Western concerns over Russia's military buildup in Syria.
Moscow says its aim is to help Syria, a longtime ally, fight the Islamic State extremist group.
Based on reporting by AFP and Interfax