BAGHDAD — Militants hung their black banners on watch towers at Iraq’s largest oil refinery, a witness said Thursday, suggesting the vital facility had fallen to the insurgents who have seized vast territories across the country’s north. A top Iraqi security official, however, said the government still held the facility. The fighting at Beiji, some 250 km north of Baghdad, comes as Iraq has asked the US for airstrikes targeting the militants from the Islamic State of Iraq and the Levant. While US President Barack Obama has not fully ruled out the possibility of launching airstrikes, such action is not imminent in part because intelligence agencies have been unable to identify clear targets on the ground, officials said. The Iraqi witness, who drove past the sprawling Beiji refinery, said militants also manned checkpoints around it. He said he saw a huge fire in one of its tankers. The Iraqi security official said the government force protecting the refinery was still inside Thursday and that they were in regular contact with Baghdad. The refinery’s workers had been evacuated to nearby villages, he said. Helicopter gunships flew over the facility to stop further militant advances, the official said. — AFP