By Rania El Gamal
BASRA, Iraq (Reuters) - A bomb attack against an Iraqi oil storage depot set one tank ablaze on Sunday in a rare assault on strategic southern oilfields, but the country's crude exports were unaffected, Iraqi oil officials and police said.
The attack underscored the complex task Iraq faces in protecting and building up its oil infrastructure as the last U.S. troops prepare to withdraw from the OPEC country at the end of the year when a bilateral security pact finishes.
Dhiya Jaffar, head of the state-run South Oil Company, told Reuters the attack set ablaze one tank at the Zubair 1 storage facility, but the explosion had not affected pumping to Al Fao port, where crude exports are dispatched.
"Production has been adjusted so daily production levels and export levels are not affected. Exports are continuing at the same rate," Jaffar told Reuters.
An Iraqi police source said bombs targeted four tanks at the facility, but only one of the tanks hit contained crude and ignited. Another bomb hit an empty tank and bombs at two other tanks were deactivated, the police source said.
Jaffar said the facility had 20 tanks, of which 14 were working. He described the attack as a "terrorist operation" without giving any details.
One Iraqi oil official said the blazing tank and another damaged tank near the Zubair oilfield, which is operated by Italy's ENI and U.S. Occidental Petroleum and South Korea's KOGAS, had been quickly isolated.
Firefighters put out the blaze hours after the attack and other storage tanks were operating normally at the complex, the Iraqi oil official said.
Crude is stored in the tanks before being pumped to Al Fao port for export. A shipping source said current exports from the area were normal at 1.632 million barrels per day.
Violence in Iraq has eased, but the country's oil infrastructure is still targeted by attacks, hampering the government's efforts to build up production and exports. Current oil output is around 2.7 million barrels per day.
Southern Iraq's oilfields have been relatively peaceful in recent years, but a bomb attack in March halted oil flows through the Iraq-Turkey pipeline in a northern area which is still a stronghold for insurgents including al Qaeda.
Militants in the north also attacked Iraq's largest oil refinery in February, killing four workers and detonating explosives that triggered a raging fire.
More than eight years after the U.S.-led invasion that toppled Saddam Hussein, the last American troops are scheduled to pull out at the end of this year. Iraqi officials say they are capable of containing internal threats.
But Iraqi commanders and U.S. officials acknowledge some gaps in the capability of Iraqi armed forces, especially in the air force, the navy and intelligence gathering.
Iraqi leaders are now debating whether some U.S. troops should stay on beyond the year-end deadline, a sensitive question testing the cohesion of Prime Minister Nuri al-Maliki's multi-sectarian power-sharing government.
(Additional reporting by Aref Mohammed in Basra and Ahmed Rasheed in Baghdad; writing by Patrick Markey; Editing by Greg Mahlich)