The Nigerian police says it is doing everything possible for the release of two Philippine oil workers seized by gunmen Tuesday.  Armed men in a speedboat kidnapped the oil workers near Nigeria's oil capital Port Harcourt.

This undated photo shows a Shell Oil rig in the Niger Delta, Nigeria (file photo)

Police spokesman Haz Iwendi, who confirmed the incident, said the police have intensified efforts for the release of the kidnapped Philippine oil workers.

"Two Filipinos were kidnapped offshore by some men when they were on their oil rig," he said.  "No group has claimed responsibility yet; we are still waiting for them.  Our men are on their trail."

Tuesday's abduction was the latest in a string of kidnappings and attacks on the Nigerian oil industry.  Ethnic Ijaw militants fighting for control of the region's resources and the release of their detained leaders have forced the closure of oil fields producing about 500,000 barrels a day since February.

But the Niger Delta Volunteer Force, a militant group led by Mujahid Dokubo-Asari, said it had suspended its violent campaigns in the delta.

Mohammed Powell, who leads the group in the absence of its jailed leader, told VOA it is considering other options to secure the release of Dokubo-Asari.

"We are tired of taking hostages and will not do it again.  We are not part of it any longer," he said.  "We are saying that we will pray till the day God will release him.  What we believe as a people is that we have not done anything wrong to the federal government or Nigerians."

Five South Korean gas workers taken hostage in the delta earlier this month were freed after a plea by the jailed militant leader in whose name they were abducted.

The Niger Delta Volunteer Force's pledge to abstain from further violence is not likely to ease the security problems in the region.

Other groups including the newly formed Joint Revolutionary Council have vowed to continue their violent protests for Dokubo-Asari's release.

Several communities in the region are equally angry with oil companies and often resort to violence to push their demands.

A total of 31 foreign oil workers, including the two Filipinos, have been kidnapped in the Niger Delta since the beginning of this year.  All previous 29 captives have been released without harm, after periods of detention from a few days to several weeks.