Militants seized two expatriate oil workers -- an American and a Briton -- during a raid on a ship off Nigeria's southern coast, an oil industry security official said on Thursday.
The armed gunmen raided the vessel off the coast of Bayelsa State and sped away in boats with the hostages, said the security official, who works for a large multinational oil company.
He declined to be named because he is not authorised to speak to the media.
Few details were available and government officials could not immediately be reached for comment.
The security official said he believed the ship belonged to the Norwegian oil firm Petroleum Geoservices.
There was no claim of responsibility and it was not known who carried out the attack.
Militants in Nigeria have launched a wave of kidnappings and attacks on oil facilities since the beginning of this year, forcing a 25 per cent decrease in crude oil production.
Nigeria traditionally produces about 2.5 million barrels of oil daily, more than any other country in Africa.
The militants say they are fighting for a greater share of oil wealth from oil companies and the government.
They say people in the area remain impoverished while oil is drawn from their land.
Dozens of foreigners have been abducted this year. The hostage-takings have usually ended peacefully, with those seized being set free after negotiations.