A drone launched by “pro-Syria regime” fighters attached U.S. backed forces in Southern Syria on Thursday, prompting a U.S. warplane to shoot it down.

This incident is the latest in a number of altercations that have placed Iranian backed militias that support Syrian President Bashar al Assad against fighters trained by the United States, the U.K. and other coalition nations.  These clashes have many concerned that a proxy war is developing in Syria, as groups with backing from several foreign nations continue to engage ISIS and increasingly, one another.

The drone, which U.S. officials claim appeared to be Iranian made, began dropping munitions near Syrian fighters who were accompanied by advisers from the American-led coalition.  The ordnance missed, and the drone was promptly shot down by a U.S. F-15E fighter.

The United States Central Command, which oversees military operations in the Middle East, said the drone destroyed on Thursday was similar in size to the U.S. MQ-1 Predator and still had unspent munitions on board when it was shot down, meaning it still posed a direct threat to Syrian fighters and U.S. advisors.