The fighting at Beiji, some 250 kilometers (155 miles) north of Baghdad, comes as Iraq has asked the U.S. to launch airstrikes targeting militants from the Islamic State of Iraq and the Levant. While U.S. President Barack Obama has not fully ruled out the possibility of launching airstrikes, such action is not imminent, officials said, in part because intelligence agencies have been unable to identify clear targets on the ground.
The Iraqi witness who drove past the Beiji refinery, said militants also manned checkpoints around it. He said a huge fire in one of its tankers was raging at the time. He spoke on condition of anonymity because he feared reprisals.
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 any militant advance, the official said. The insurgent took over a building just outside the refinery and were using it to fire at the government force, he said.
The Beiji refinery accounts for a little more than a quarter of the country's entire refining capacity — all of which goes toward domestic consumption for things like gasoline, cooking oil and fuel for power stations. Any lengthy outage at Beiji risks long lines at the gas pump and electricity shortages, adding to the chaos already facing Iraq.
The campaign by the al-Qaida-inspired Islamic State militants has raised the specter of the sectarian warfare that nearly tore the country apart in 2006 and 2007, with the popular mobilization to fight the insurgents taking an increasingly sectarian slant, particularly after Iraq's top Shiite cleric made a call to arms on Friday.
The Islamic State has vowed to march to Baghdad and the Shiite holy cities of Karbala and Najaf, home to some of the sect's most revered shrines, in the worst threat to Iraq's stability since U.S. troops left in late 2011. The militants also have tried to capture Samarra, a city north of Baghdad and home to another major Shiite shrine.
In an incident that harkens back to the dark days of Iraq's sectarian bloodletting of 2006 and 2007, the bullet-riddled bodies of four men, presumably Sunnis, were discovered in the Shiite Baghdad district of Abu Dashir on Thursday, police and morgue officials said. The bodies were handcuffed and had gunshot wounds to the head and chest.
Also in Baghdad, a roadside bomb hit a police patrol on a highway in the east of the city, killing two police officers and wounding two, police and hospital officials said. Earlier Thursday, a car bomb exploded inside a parking lot in Baghdad's southeastern Shiite neighborhood of New Baghdad, killing three people and wounding seven, the officials said.
All officials spoke on condition of anonymity because they were not authorized to speak to the journalists.
The U.S. has pushed Iraq to present its people a clear coalition to fight the militants, with Vice President Joe Biden offering praise Wednesday for Iraq's Shiite, Sunni and Kurdish leaders as a means to tamper the sectarian anger roiling the country. It's unclear whether that will work, as Iraqi Prime Minister Nouri al-Maliki's Shiite-led government has faced widespread dissatisfaction from the nation's sizable Sunni and Kurdish minorities.
Al-Maliki, a Shiite, has rejected charges of bias and instead said the crisis has led Iraqis to rediscover "national unity."
"I tell all the brothers there have been negative practices by members of the military, civilians and militiamen, but that is not what we should be discussing," al-Maliki said Wednesday. "Our effort should not be focused here and leave the larger objective of defeating" the militants.
Still, al-Maliki's outreach remain largely rhetoric, with no concrete action to bridge differences with Sunnis and Kurds, who have been at loggerheads with the prime minister over their right to independently export oil from their self-rule region in the north and over territorial claims.
Iraqi Foreign Minister Hoshyar Zebari said Wednesday that his country had formally asked the U.S. to launch airstrikes against positions of the Islamic State.
Gen. Martin Dempsey, the chairman of the U.S. Joint Chiefs of Staff, confirmed the U.S. had received a request for air power to stop the militants, but highlighted the uncertain political situation in Iraq.
"The entire enterprise is at risk as long as this political situation is in flux," told a Senate panel Wednesday. He added that some Iraqi security forces had backed down when confronted by the militants because they had "simply lost faith" in the central government in Baghdad.