BAGHDAD - Iraq's Popular Mobilisation Forces, a grouping of mostly Iran-backed Shi'ite paramilitaries, said on Monday a US air strike on the Iraqi border with Syria killed 22 of its members and wounded 12 others. 'At 8 p.m. last night a US plane hit a standing headquarters of the Popular Mobilisation Forces defending the border strip with Syria using two guided missiles which lead to the martyrdom of 22 fighters,' it said in a statement. It demanded an explanation from the United States.