LAGOS, Nigeria - Gunmen kidnapped a group of foreign oil workers on Friday, including three Americans and four Britons, in Nigeria's unruly southern petroleum-producing region, officials said.

An oil rig in a file photo. Oil rose to $71 a barrel on Friday, near a nine-month high, as a strike in Nigeria threatened more of the country's output and Iran remained defiant over its nuclear programme. [Reuters]

Security forces in the region earlier said only six people were kidnapped, including an Indian, but details released by U.S. and British embassy officials put the number at at least seven.

The embassy officials both spoke on condition of anonymity, citing standard agency prohibitions againts their names appearing in public.

The latest abduction to hit Africa's oil giant took place in southern Bayelsa state, said Joshua Benemesia, a leader of an unarmed, government-funded group that helps provide security in the state. He said six foreigners were taken, including an Indian. All were aboard a boat owned by a Nigerian oil-services company, he said.

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.

Security forces were trying to make contact with the hostage takers, who grabbed the man on his way to work in the southern city of Warri on Thursday, said Brig. Gen. Lawrence Ngubane, a military commander in the region.

The kidnappings are the latest in a run of more than 100 seizures of foreign workers this year in the oil-producing Niger Delta, where all of the crude is pumped in Africa's largest producer.

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're 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 and a top supplier of crude to the United States.