20100110

ABUJA (Reuters) - Chevron said on Saturday it had been forced to shut down 20,000 barrels per day (bpd) of crude oil production in Nigeria, a day after security sources said gunmen had attacked a pipeline operated by the U.S. firm.

"Chevron Nigeria Limited ... confirms that there was a breach on its Makaraba-Utonana pipeline in Delta State, Nigeria on Friday," the major U.S. oil producer said.

Security sources told Reuters on Friday that unknown gunmen in the oil-rich Niger Delta attacked the pipeline, which has been vulnerable to sabotage in the past. No group has claimed direct responsibility.

"This attack was sanctioned by MEND, but did not involve our fighters," the Movement for the Emancipation of the Niger Delta, the main militant group operating in the region, said in a statement.

Militant attacks on the oil industry in the vast wetlands region have prevented the OPEC member from pumping much above two-thirds of its 3 million bpd production capacity, costing it an estimated $1 billion a month.

The pipeline attack comes five days after four Chevron workers in Delta state were killed in a shooting incident involving the military, said Oma Djebah, spokesman for the state government.

Violence in the Niger Delta has subsided for the past few months after thousands of gunmen handed over their weapons and accepted an amnesty offer from President Umaru Yar'Adua.

Thousands of guns, grenades and rounds of ammunition were surrendered under the amnesty, but security sources said from the start that peace would only last if those who disarmed were quickly re-trained and found work. But progress has been slow.