Chevron has been forced shut down oil production at its Escravos terminal in Nigeria following an attack by militants, the second time in recent weeks that violence has impacted the oil giant's facility in the Niger Delta region.
A militant group called the Niger Delta Avengers, which has told oil firms to leave the oil-rich delta before the end of May, said late on Wednesday that it had blown up the onshore facility's main electricity feed.
"It is a crude line which means all activities in Chevron are grounded," a Chevron source told Reuters on Thursday, without elaborating.
The Avengers posted a message on Twitter claiming responsibility for the attack.
A Chevron spokeswoman in the United States said on Thursday that it was against policy to comment on the safety and security of personnel and operations.
Industry sources said that Escravos onshore production accounts for roughly a third of its total output, on average 3.8 million barrels per month (bpm) in 2014, according to the latest available data from the Nigerian National Petroleum Corporation.
The Avengers and other militants — who say they are fighting for a greater share of oil profits, an end to pollution, and independence for the region — have intensified attacks in recent months, pushing oil output to its lowest in more than 20 years and compounding the problems faced by Africa's largest economy.
In February the group claimed an attack on an undersea pipeline, forcing Shell to shut a terminal that produces 250,000 barrels of oil per day.
In early May, Escravos production was already down by more than 40,000 bpd after a May 5 militant attack on a Chevron offshore facility. The Avengers took credit for blasting the Chevron platform earlier this month, shutting the Warri and Kaduna refineries.
There have been other smaller attacks, and another explosion this month that closed Shell's Bonny Light export program bore the hallmarks of the group.
Increased violence over the past few weeks has made international buyers more reluctant to buy Nigerian crude due to fears of loading delays and cancellations.
Nigerian authorities have responded by moving in army reinforcements, but British Foreign Minister Philip Hammond said this month that President Muhammadu Buhari needed to deal with the root cause of the insurgency.
Delta residents, some of whom sympathize with the militants, have complained for years about widespread poverty in an area that accounts for 70 percent of Nigeria's national income.
Buhari has extended an amnesty deal signed with militants in 2009 that stepped up funding for the region. The deal channeled more state cash to the region for job training, and handed contracts to militant groups to protect the pipelines they once bombed. But Buhari cut the budget allocated to the plan by about 70 percent and canceled the contracts, citing corruption and mismanagement of funds.
Cutting of the amnesty plan's budget, which devoted funds for job training for the unemployed, has also caused widespread resentment in the Delta. Tapping into such anger, the Avengers point out that the former military ruler has never visited the Delta, where many roads are pot-holed and some villages are polluted from oil spills.
Buhari has said he will crush the militants, but a wide-scale conflict could stretch security forces already battling the Boko Haram militant group in Nigeria's north.
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