Armed militants have begun attacks on oil installations in Nigeria's volatile Niger Delta after warning they would do so. The fighters are protesting the arrest of their leader who is being held in the capital, Abuja. Joe Bavier has this report from VOA's West Africa bureau in Abidjan.

Dozens of armed separatists sped in boats toward Niger Delta oil installations owned by U.S.-based oil firm Chevron. Fighters said they had taken over the Idama flow station and forced it to shut down.

One commander said they would take over other installations and threatened to set them on fire or blow them up.

Members of Mujahid Dokubo-Asari's Niger Delta's Peoples Volunteer Force had called for their leader's release.

Mujahid Dokubo-Asari looks on as he appears before a court in Abuja, Nigeria, Sept. 22, 2005

But a high court in Nigeria's capital, Abuja, instead ordered Mr. Asari to remain in detention for two weeks while charges of treason are prepared against him. The charges stem from a newspaper interview in which he is alleged to have called for the dissolution of Nigeria.

Militants say thousands of their supporters are ready to be armed if he is not released, and some are patrolling the intricate system of creeks in the Niger Delta.

Military officials, who began setting up checkpoints for security this week, say they are ready to defend oil pipelines and wells.

But faced with the growing threat of violence, some oil companies say they are removing employees from sensitive areas and are restricting the travel of others.

Last year, Mr. Asari announced, what he called, a full-scale war on foreign oil interests. The situation was calmed after President Olusegun Obasanjo met with him personally. The militant leader promised to disarm in exchange for government help.

But an advisor to Delta State traditional rulers, Ologorun Atuyota Ejuhnre, says a lack of follow-up on government promises have spawned further resentment in a region that has remained impoverished despite rich natural resources.

"Apparently I do not think that much has been done," he said. "In fact, some of the papers have carried some publications that a lot of militias were being trained, about 6,000 young persons, who have been training with a view of declaring a republic of the Niger Delta."

Federal troops have been accused of violent crackdowns and human rights violations in their attempts to pacify the Niger Delta. Mr. Ejuhnre says the government's decision to bolster its presence there may end up causing more harm.

"In my personal view, it will exacerbate the situation, because foot soldiers are likely to react rather negatively and violently. And I think a solution should be more of negotiation than clamping down," he said.

The Niger Delta has long been the scene of violent confrontations between federal troops and local militias. The armed groups are demanding a bigger share of oil revenues and blame foreign firms for widespread environmental destruction.