US Central Command said the strikes were against "Iran-aligned terrorists that the Islamic Revolutionary Guard Corps directed to attack US forces and Saudi energy infrastructure".
Iraq's paramilitary Popular Mobilisation Forces, which is dominated by Iran-backed Shia militias, said at least 20 of its members had been killed in US-Saudi strikes on its bases.
It came hours after Centcom said Iran had launched missiles at US forces in the Middle East in an "attempted surprise attack", ending a lull in hostilities.
