LAGOS, Nigeria &

Gunmen on Friday seized a boatload of foreign oil workers, including three Americans, four Britons and a South African, in the latest violence to hit Nigeria's southern petroleum-producing region, officials said.




Nearly 200 foreign workers have been kidnapped in 18 months of attacks on oil companies and security forces in the Niger Delta, where all the crude is pumped in Africa's biggest producer.




The latest seizures came when gunmen stormed a boat owned by a Nigerian oil-services company as it carried the foreigners in the vast region of mangrove swamps and creeks, security force officials said.




U.S. Embassy officials said three Americans were taken and the British embassy reported four Britons missing after the attack. One South African was also taken, Pretoria said.




Security forces in the region earlier said only six people were kidnapped, including an Indian.




U.S. and British embassy officials spoke on condition of anonymity, citing embassy prohibitions against their names appearing in public.




On Thursday, five gunmen grabbed a Polish worker heading to his construction project in southern Nigeria and rushed the captive into the lawless oil-rich region's swamps and creeks in a speedboat, officials said.




Over a dozen foreigners seized in the region are currently in captivity.




Some 200 foreign workers have been taken since militants stepped up their attacks against the oil companies and government in late 2005, cutting nearly one-third of Nigeria's daily crude production capacity and sending oil prices toward historic highs in oversees markets.




The militants say they are fighting for the liberation of two of their leaders imprisoned on corruption and treason charges and more oil revenues for their impoverished lands.




But in recent months, criminal gangs have taken up the practice of kidnapping foreigners for ransom. Hostages are generally released unharmed after a payment is made to the captors, although two died in the crossfire when security forces intervened.




Nigeria is Africa's biggest oil producer, an OPEC member, and a top supplier of crude to the United States.




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Associated Press Writer William Nsoyoh in Yenagoa, Nigeria contributed to this report.