Over 15,000 militants who laid down their arms in Nigeria's restive oil region have so far been registered but the number could rise at the end of documentation, Nigerian defence minister said Sunday.

"Although our projection based on initial assessment estimated the figures of all true militants as 17,000, the number we have now is 15,260," General Godwin Abbe told reporters in Lagos.

"These figures cannot be categorical at this stage of the upsurge in the number of ex-militants since the end of the amnesty period. Some of the groups are yet to authenticate their lists," he said.

Although our projection based on initial assessment estimated the figures of all true militants as 17,000, the number we have now is 15,260

General Godwin Abbe

He said "contacts are ongoing" to get those yet to lay down their arms after the expiration on October 4 of the 60-day amnesty.

Information and Communications Minister Dora Akunyili said the unconditional pardon of the fighters, whose violent activities played havoc with the international oil market, was a success.

"The successful conclusion of the amnesty deal is the culmination of honest and all inclusive dialogue between the federal government and diverse stakeholders in the Niger Delta," she said.

"The achievement is unprecedented, not only in the history of Nigeria, but also throughout the world, in places where such internal disorders have occurred," she said.

She urged further cooperation with the government in order to move to the post-amnesty stage of rehabilitating and reintegrating the ex-militants.

"As we celebrate the success of this landmark event, government is not unmindful of challenges of the post-amnesty phase that lie ahead," the minister said.

She said government was determined to take all necessary steps to vigorously address the challenges of underdevelopment and injustice in the Niger Delta.

Attacks on oil facilities since the beginning of 2006 have reduced Nigeria's oil output by a third and helped send oil prices sky-rocketing to the July 2007 record high of 147 dollars a barrel.

The main armed group in the Niger Delta, MEND, on Sunday declared an "indefinite ceasefire" to encourage dialogue with the government, but the government said it it would not recognise mediators that the group appointed.

MEND, which says it is fighting for a greater local share of the region's oil wealth, said it has put together a team to discuss its demands with the government, including Nigerian Nobel literature laureate Wole Soyinka.