Russia says US-led coalition air strikes have killed more than 60 Syrian soldiers in the northeastern city of Deir el-Zour.
"The state forces of the Syrian Arabic Republic have been attacked by the planes of the international coalition, led by the United States of America, in the area of Deir el-Zour," said Sergei Rudskoi, Russian Ministry of Defense.
"As a result, many are dead. This incident was possible because of poor awareness by the coalition and its unwillingness to coordinate its actions against terrorist groups in Syria. We are waiting for an explanation from the military commanders of the aviation group, headed by the US."
The US military admits they carried out the raids and says they mistook government forces for ISIL targets. The United Nations Security Council has held an emergency meeting on the air strikes.
Moscow says the incident puts the ceasefire -- brokered by the US and Russia -- in jeopardy. The ceasefire took effect on Monday. There have been repeated accusations of violations on both sides.