Four US oil workers have been kidnapped in Nigeria's volatile Niger Delta, only hours after 11 Korean and Filipino workers were freed.
Armed men in speed boats seized the workers from a barge near an oil export terminal belonging to Chevron.
On Tuesday, the main militant group in the oil-rich south said it blew up three oil pipelines in Bayelsa State, the most damaging attack for a year.
Militants have now cut Nigerian oil production by almost a third.
The price of oil in London has moved up to almost $66 a barrel.
"Armed men on two speed boats with rifles and RPGs (rocket-propelled grenades) boarded (the barge). Four American personnel were abducted," a source who asked not to be named told Reuters news agency.
The kidnapping is the ninth attack in nine days.
Nearly 100 foreign workers have been abducted this year and 13 are in captivity.
Warning
Many of those kidnapped in the Delta are seized by armed gangs wanting ransom money and they are released unharmed once a payment is made.
But the militant group, Mend, says it wants a larger share of oil wealth for local communities and recently warned that they would step up attacks on oil installations in the region as "parting gift" to President Olusegun Obasanjo who stands down in three weeks time.
MEND
They say the oil pipeline attacks on Tuesday were also in pursuance of their resolve to cripple the Nigerian crude oil export industry.
Mend says it will continue its renewed campaign "indefinitely with attacks on all pipelines, platforms and support vessels".
The BBC's Alex Last in Lagos says with the new Nigerian government about to be installed at the end of the month, the timing of the escalating violence is crucial.
He says armed gangs and militants want to be seen as key players by the incoming administration.
Meanwhile, some military personnel have been arrested in the Niger Delta suspected of collaborating with militants.
The eight Filipinos and three South Koreans, all workers at Daewoo, had been taken at gunpoint from a heavily guarded compound last Thursday.
South Korean government officials said the freed hostages were well.
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