Nigerian military personnel were said to have fought the attackers but were unable to stop the abductions.
 
The Joint Task Force, the military unit in charge of policing the Niger Delta oil region, said it suffered no casualties during the attack.
 
Nigeria: recent kidnappings

April 7 - Two Turkish engineers kidnapped from their car in Port Harcourt.

April 27 - Two policemen killed in a failed kidnap attempt in Port Harcourt, the officers were escorting a convoy of vehicles carrying expatriate staff to work.

May 1 - Six oil workers kidnapped from an offshore oil facility operated by Chevron

May 3 - 20 foreign workers kidnapped in three attacks in the Niger Delta but eight are freed within hours

May 5 - British oil worker from Trident 8 rig abducted, gunmen also abduct a Belarussian woman, working for UK's Compass Group, from outside her residence in Port Harcourt.

May 8 - Three South Koreans and eight Filipinos freed after being held for five days

A spokesman for Chevron said the oil workers were all US nationals, but a US diplomat later said there was a possibility one of the men was Canadian.
 
No one has claimed responsibility for the new attack.
 
More than 30 foreigners have now been kidnapped in the Niger Delta this month. There had been a lull in kidnappings during the Nigerian elections last month.
 
The attack follows the sabotage of three pipelines on Tuesday by southern Nigeria's most high-profile armed group, the Movement for the Emancipation of the Niger Delta (Mend), which has vowed to keep up its attacks on oil targets.
 
Mend, whose 18-month campaign of attacks has forced the closure of almost a third of Nigeria's oil capacity, threatened to launch more before Olusegun Obasanjo, Nigeria's current president, steps down and Umaru Yar'Adua takes over on May 29.
 
"We promised to send Obasanjo off in shame and that is what is happening," said Mend's spokesman, who uses the pseudonym Jomo Gbomo.
 
The Niger Delta area is at the centre of a long confrontation between the government and a large number of armed groups, many of which say they are fighting for a larger share of the country's oil resources for local people.