A rare US airstrike in Syria has killed approximately 100 pro-government troops.
Military officials said the strike was launched after as many as 500 attackers began an assault on opposition forces accompanied by US advisers in Deir el-Zour province.
Artillery and tank rounds were used by pro-Bashar Assad soldiers against the US-backed Syria Democratic Forces on Wednesday.
No US service personnel were injured or killed but one SDF member was wounded.
About 100 of the attackers were then killed in a counter-strike, an American military official said.
The SDF, aided by coalition support, are battling so-called Islamic State militants east of the Euphrates River. Syrian government forces are active on the other side of the river around the city of Deir el-Zour.
Officials said it appeared that the pro-regime forces were trying to take back land that the SDF had liberated from IS fighters last September, including oil fields in Khusham.