Later Tuesday, Dokubo-Asari's deputy in the Niger Delta People's Volunteer Force, Alali Horsefall, said that if the government "doesn't release my president within 24 hours, they will see danger." He said the militia would "blow up oil installations" if Dokubo-Asari was not released by 2 p.m. and warned foreign oil workers to leave the area.

Nigeria is the world's eighth largest oil exporter, and the fifth main supplier to the United States. Last year, threats by Dokubo-Asari to unleash a "full-scale war" and target international oil firms helped send world oil prices to then-record levels. Fighting involving Dokubo-Asari's group, other armed militias and Nigerian security forces killed hundreds last year, before he agreed to disarm under a September 2004 peace deal. His group says the people of the Niger delta, including his own Ijaw ethnic group, should break away from Nigeria and take control the billions of dollars of oil flowing from their land. Dokubo-Asari's apparent arrest comes at a tense time in the Niger Delta.

Another prominent militant group has issued veiled threats against Britons after the governor of the Niger delta state of Bayelsa was arrested for questioning in Britain over suspicions of money laundering.

Niger Delta rebels in a boat