The United States is telling pro-Syrian government forces to move away from an area near the Jordanian border where the coalition is training allied rebels.
The warning comes less than two weeks after the Americans bombed Iranian-backed troops there who didn't heed similar warnings.
Navy Capt. Jeff Davis, a Pentagon spokesman, says the U.S. dropped leaflets over the weekend telling the forces to leave the established protected zone.
Davis says the U.S. has seen pro-Syrian government militias patrolling and gathering in the desert around Tanf. The area has been considered a "deconflicted" zone under a U.S.-Russian understanding.
Davis says "hundreds" of pro-government forces are in the region.