The Pentagon says the U.S.-led coalition fighting the Islamic State group has struck what it calls pro-government forces in Syria.
It says Tuesday's attack occurred after forces supporting Syrian President Bashar Assad entered an area near a coalition base in southern Syria with a tank, artillery, anti-aircraft weapons, other vehicles and more than 60 soldiers.
A statement says the pro-Assad forces ignored several coalition warnings.
The Pentagon statement didn't further identify the targeted forces.
But in recent weeks, officials have complained about various militants refusing to leave an area near Tanf, Syria.
The U.S. and its partners train Syrian rebels there to fight ISIS.
The coalition struck similarly described forces in the area last month.