Syria’s ceasefire was hanging by a thread on Sunday, after tensions escalated between Moscow and Washington over a U.S.-led coalition air strike that killed dozens of Syrian soldiers.
The Syrian Observatory for Human Rights said at least 90 soldiers were killed in the strike. Moscow put the death toll at 62.
The Syrian Army said the raid on Saturday had allowed Islamic State (IS) group fighters to gain ground around the key eastern airbase of Deir Ezzor.