The Syrian Foreign Ministry on Thursday condemned the US-led airstrikes on pro-government forces in the eastern province of Deir al-Zour, state news agency SANA reported.
In a statement, the ministry accused the US warplanes of "committing a massacre" against pro-government forces that were confronting the Islamic State (IS).
Calling it a "new barbaric aggression", the ministry said the US attack came in the framework of Washington's "aggressive policies" against Syria, Xinhua reported.
The pro-government Syrian forces were confronting IS, "who are under the protection" of the US coalition and the allied forces of the Syrian Democratic Forces (SDF), it added.
The Syrian government urged the UN Security Council to condemn the massacre and to hold the US coalition responsible for their "crimes and aggression that have left thousands of civilians either killed or wounded," the statement said.
Earlier in the day, the SDF said the US-led coalition struck positions of pro-Syrian government forces in the eastern Syrian province of Deir al-Zour to defend its partners.
The coalition's move was in retaliation for the pro-Syrian government forces' targeting of the U.S.-backed forces in the area, the SDF noted.
Meanwhile, SANA reported that U.S. warplanes carried out 10 airstrikes on the positions of the pro-government forces after midnight on Saturday.
According to the London-based Syrian Observatory for Human Rights, at least 45 pro-government fighters were killed in the airstrikes.
Meanwhile, a statement from Deir al-Zour's Syrian tribes said the US coalition airstrikes killed their young fighters who were battling IS and the SDF on the eastern bank of the Euphrates River.
The tribes of Deir al-Zour will continue to fight the terrorists until their areas taken by the IS and the SDF on the eastern bank of Euphrates are all liberated, the statement added.