U.S.-backed Syrian militias accused the Syrian government on Monday of bombing their positions southwest of Raqqa city in recent days and threatened to retaliate if the attacks continue.

Axar.az reports citing Reuters.

"The regime's forces...have mounted large-scale attacks using planes, artillery, and tanks," Syrian Democratic Forces spokesman Talal Selo said in a statement.

A U.S. warplane shot down a Syrian army jet on Sunday southwest of Raqqa, with Washington saying the army had dropped bombs near U.S.-backed forces and Damascus saying the plane had been flying a mission against Islamic State militants.

There was no immediate comment from the Syrian army.