US and international forces in northeastern Syria were attacked with drones and rockets at least four times in the past 24 hours, though there were no casualties , a US military official said on Monday. US forcescame under attack three times on Sunday evening, including near the Al Omar Oil field and at a US base at al-Shaddadi, the official said. Multiple drones were fired at US forces at the Rumalyn Landing Zone on Monday, the official said.The attacks came after the US carried out two air strikes on Sunday against facilities it said were used by Iran-aligned groups, its third set of strikes in Syria in as many weeks. US and coalition troops have been attacked at least 40 times in Iraq and Syria since early October. So far, at least 56 US personnel have suffered everything from minor wounds to traumatic brain injuries, the Pentagon has said. The US blames the attacks on groups backed by Iran – an assertion denied by Tehran.