Heavily armed gunmen kidnapped four US oil workers from a barge off the Nigerian coast on Wednesday as violence flared after disputed elections in the world's eighth largest oil exporter.
It was the tenth attack on Western oil facilities in nine days in the Niger Delta, home to Africa's biggest oil industry, and comes in the wake of April's general elections, which were condemned by observers as fraudulent.
Some militants have stepped up attacks to make clear they are unimpressed by the looming change in government, despite the election of a state governor from the delta as vice president. Others may be taking advantage of a reduction in security after the polls to resume their criminal pursuits, analysts say.
"The Global Cheyenne, a construction barge working in the Okan field, was attacked by unknown armed persons in speed boats," US oil company Chevron said in a statement.
"Four expatriate American hostages were taken from the vessel and some government security forces suffered injuries during the attack," it added. No group has claimed responsibility for the latest attack, which helped push London Brent crude prices near $66 a barrel on Wednesday morning. Prices later eased. The barge, operated by US contractor Global Industries, was laying pipelines for the US giant and oil supplies were unaffected.