Militants attacked and shut down Iraq's largest oil refinery on Saturday, killing four workers and setting off bombs that started a raging fire, officials said.
The assailants broke into the Beiji refinery around 3:30 a.m. local time, attacking guards and planting explosives.
"The refinery has completely stopped," Salahuddin province Governor Ahmed al-Jubouri told Reuters. "It's a big loss for the whole country. All Iraqi cities depend on its production."
A former al-Qaida stronghold, Beiji is about 155 miles north of Baghdad.
The blast sparked a fire that was later brought under control, a police source said. It took about five hours and up to 50 fire trucks to contain the blaze.
The units that were damaged by the attack have a production capacity of around 150,000 barrels per day, a Beiji official said.
"Fixing the damage will take long time. We are not talking about days, the damage is too severe," said the Beiji official, who asked not to be named.
Iraq does not export any oil products as it uses all of its production for power generation and domestic consumption.
The country's capacity to refine fuels like diesel and gasoline has been ravaged by underinvestment, and it has been forced since the 2003 U.S.-led invasion to buy imported fuels to meet the growing gap between supply and domestic demand.
Baghdad has signed multi-billion deals with international oil companies to boost output capacity to 12 million barrels a day in seven years, rivaling top oil exporter Saudi Arabia.
But everything depends on whether the OPEC member can secure its vital oilfields, refineries and other infrastructure against insurgents and militia that have plagued the country since the invasion.
Overall violence in Iraq has dropped sharply since the peak of sectarian conflict in 2006-07 but attacks still occur on a daily basis.
The Beiji refinery was previously controlled by al-Qaida militants, who used it to finance the insurgency.
Beiji normally operates at 70 percent of its capacity and produces 11 million liters of gasoline, 7 million liters of benzene and 4.5 million liters of kerosene a day. The refinery was last shut in August for two days due to an electrical fault.