A major pipeline used by Royal Dutch Shell Plc's two main oil export terminals in southern Nigeria was attacked and ruptured by the unknown.
Precious Okolobo, a spokesman for Shell in Lagos, said the affected pipeline supplies crude oil to the Forcados oil export terminal. He would not give further details on the nature of the attack and when it was carried out.
The main militant group fighting in the oil region claimed responsibility for the attack.
"We will continue to nibble on the oil industry until they feel the pains," the Movement for the Emancipation the Niger Delta, or MEND, said in an e-mail to The Associated Press.
Oil exports through Forcados had suffered in the past two years as attacks by armed groups in the main oil-producing Niger Delta region forced shut many of the oil fields supplying the terminal, which can handle 400,000 barrels of crude daily.
A lull following the emergence of President Umaru Yar'Adua in May and a cease-fire called by MEND enabled Shell to restart production in some of the abandoned fields.
MEND, which claims to be fighting for a greater share of oil wealth for the delta's impoverished inhabitants, ended its cease-fire after one of its leaders, Henry Okah, was arrested in Angola in September on gunrunning charges the group said were instigated by Nigeria.
The group said on Wednesday it was embarking on a bloody, new phase. It claimed responsibility for an attack targeting an ExxonMobil facility on Monday, but denied responsibility for another raid the same day in a nearby border area in which 21 Cameroonian troops were killed.
The attack on a military position outside ExxonMobil's Qua Iboe oil export terminal on Monday was aimed at seizing weapons and equipment, and was a success, MEND said in the e-mail, sent Wednesday night. The group alleged Nigerian troops had attacked the Cameroonian positions in formerly disputed Bakassi peninsula "because of their perceived sympathy to our cause and their blind eye to a weapons route."
Nigeria denies the allegation, and has in turn blamed the militants for the attack.
Attacks by MEND and other armed groups in the oil region have cut Nigeria's oil exports of 2.5 million barrels daily by more than 20 percent in the last two years.
Nigeria is Africa's leading oil exporter and the fifth-biggest source of U.S. oil imports.
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