ABUJA: Nigeria's main militant group said Wednesday it is calling an immediate 60-day cease-fire in response to the government's release of an ailing rebel leader.

Henry Okah was freed Monday just hours after the Movement for the Emancipation of the Niger Delta set fire to an oil depot and loading tankers in the country's economic center, Lagos.

Three naval officers and two oil workers were killed in the group's first attack outside the Delta region, officials said.

The insurgents said in a statement that they hope the cease-fire, to take effect Wednesday, will create an "enabling environment" for negotiations.

Okah's release was one of several rebel demands. The statement said talks can only begin after the military withdraws and people forced from their homes are allowed to return.

Rebel attacks on oil installations and kidnapping of foreign oil workers for ransom have cut output of Africa's biggest oil producer by a quarter and often affect world oil prices.

Okah is the first militant released under a 60-day amnesty announced last month for militants willing to lay down their arms. MEND rejected the offer, saying an amnesty should be aimed at criminals, not "freedom fighters."

Militant groups in the Delta region say they are fighting to force the federal government to devote more oil revenue to the southern region, which remains poverty-stricken and polluted more than 50 years after oil first was pumped in the West African nation.

The government says most militants are criminals using politics to mask the lucrative theft and overseas sale of crude oil stolen from Nigeria's network of wells and pipelines.

MEND initially said Okah's release would not end its attacks but that "MEND considers this release as a step towards genuine peace and prosperity if Nigeria is open to frank talks and deal sincerely with the root issues once and for all."

Wednesday's statement said the cease-fire was decided on "several factors ... chiefly the release of Mr. Henry Okah." It said a group of wise women and men is being put together to present the government with its demands and those of other stakeholders.

Okah was arrested in Angola in September 2006 and repatriated to Nigeria to face charges of treason and gunrunning. His lawyer, Femi Falana, said the government has dropped the charges.

MEND has said Okah has a kidney ailment that needs urgent medical treatment abroad.

On his release, Okah told reporters he could not say if he could help end the conflict.

"I have to see people, speak with people," Okah said. "I am just one man; there are millions in the Niger delta."