An air strike carried out by the US-led coalition in Syria is reported to have targeted the Syrian army for the first time, killing at least three soldiers and destroying a number of vehicles.
The Syrian government said four warplanes bombed its Saega military camp in Deir al-Zor province, describing it as an "act of aggression" by coalition forces.
According to the Syrian Observatory for Human Rights monitoring group, 13 more military personnel were wounded in the strike, which it said took place near the town of Ayyash on Sunday evening.
But while the Syrian foreign ministry said in a statement that it had written to the UN over the incident, a spokesman for the coalition denied it had carried out any air strikes on the area in question.
The US-led coalition has been bombing the largely Isis-held region of Deir al-Zor since it began its campaign against the militant group.
But if confirmed, Sunday's attack would be the first time a coalition bombing raid had, accidentally or otherwise, targeted the forces of Syrian President Bashar al-Assad.
The Syrian foreign ministry said: "Syria strongly condemns the act of aggression by the US-led coalition that contradicts the UN Charter on goals and principles. The Ministry of Foreign Affairs has sent letters to the UN Secretary General and the UN Security Council."
It urged the UN to take "immediate action and take the necessary measures to prevent a repeat" of the incident.
Speaking to the AFP News Agency, however, Col Steve Warren at the joint coalition command centre said the allied forces' only strikes in Deir al-Zour on Sunday were more than 30 miles away from the camp named in monitoring reports.
"We've seen those Syrian reports but we did not conduct any strikes in that part of Deir al-Zour yesterday," he said. "So we see no evidence."
He did not provide comment on reports from the Observatory that a second coalition strike on Sunday destroyed a building in Deir al-Zor city itself, killing a woman and two children.
An eastern province in Syria, Deir al-Zor represents a key link for Isis between its Raqqa stronghold and territories in Iraq.