By Estelle Shirbon

LAGOS, Feb 20 (Reuters) - A rebel group from Nigeria's oil producing Niger Delta demanded on Wednesday that lawyers, relatives and the Red Cross be allowed to see their detained leader, Henry Okah, to confirm he is alive.

The government denied late on Tuesday a report by the rebel Movement for the Emancipation of the Niger Delta (MEND) that Okah had been shot dead in detention in northern Nigeria. The president's spokesman said he was "alive and in safe custody".

Uncertainty over Okah's fate since he was handed over to Nigeria from Angola last Thursday has been raising tensions in the delta, home to Africa's biggest oil industry which produces 2.1 million barrels per day.

The MEND's anger over what it sees as government persecution of Okah risks triggering a new round of violence and derailing tentative peace talks between the government and several delta militant groups.

"Following the weak denial by the Nigerian government spokesman over the killing of Comrade Henry Okah, the government must go a step further," the MEND said in an email to journalists.

"(It must allow) access to his legal representatives, family, pastor and the International Red Cross or similar body for an independent verification that he is alive and has never been tortured."

Government spokesmen were not immediately available for comment.

The MEND is one of several armed groups who say they are campaigning to redress injustice in the impoverished delta, where five decades of oil extraction have brought pollution and corruption but few benefits for the poor majority of residents.

Militancy and crime are intertwined in the delta and the same groups that make demands for local control of oil resources or greater political autonomy also seek profits from kidnappings for ransom, smuggling stolen crude, and extortion rackets.

Okah's MEND rose to prominence in early 2006 when he led a wave of pipeline bombings and hostage takings of oil workers that forced the closure of a fifth of Nigerian oil output.

In May 2007, President Umaru Yar'Adua came to power promising peace talks with delta militants, and at first Okah's group was receptive. It declared a temporary ceasefire.

But in September, Okah was arrested in Angola on gun-running charges and his group resumed attacks and threats.

Last Friday, the MEND and the Angolan state news agency reported Okah had been handed over to Nigeria but there was no comment from the Nigerian authorities until Tuesday night's denial that he had been shot dead in detention.

The leaders of other militant groups have returned to the negotiating table this month after a hiatus lasting a few weeks, but anger over the government's handling of Okah could again jeopardise progress. (Reporting by Estelle Shirbon; Editing by Michael Winfrey)

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