U.S. officials say America launched airstrikes on Syrian government-backed troops Wednesday after they attacked Syrian opposition forces who were accompanied by U.S. advisers in Deir el-Zour Province.

It's a rare strike against forces that support Syrian President Bashar Assad's regime. The U.S.-backed Syrian Democratic Forces, aided by coalition support, are battling 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.

The U.S. coalition says in a statement that pro-regime forces attacked an SDF headquarters, and the U.S. launched the airstrike in self-defense.

U.S. officials say no Americans were injured or killed in the attack by the pro-regime forces. They spoke on condition of anonymity as details are still emerging on the attack.