Nigerian gunmen attack Lagos dock, top rebel freed

* Main rebel group claims rare attack outside Niger Delta

* Gov't frees suspected MEND leader Henry Okah

* Security sources prepare for more violence

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By Tume Ahemba and Shuaibu Mohammed

LAGOS/JOS, Nigeria, July 13 (Reuters) - Nigeria's main militant group widened its offensive against Africa's biggest oil sector on Monday despite the release of its suspected leader, raising concern there might be further attacks.

The Movement for the Emancipation of the Niger Delta (MEND) sabotaged an oil offloading dock in Lagos state, killing five people in the group's first attack outside the Niger Delta since it began its latest campaign of violence.

The expansion of MEND's range has heightened security concerns beyond the oil industry and dashed hopes that the release of its suspected leader, Henry Okah, would halt the militant offensive, analysts said.

"What the government has done in the case of Okah is like treating the symptom and not curing the disease," said Abubakar Momoh from Lagos State University.

"That will not put an end to militancy because there are many Henry Okahs there, except that they are not as well known."

MEND said its fighters set the depot ablaze overnight at the Atlas Cove Jetty in Lagos, a key port where ships unload imported gasoline, diesel and other products.

"We were taken by surprise because the facility is well secured," Mohammed Barkindo, managing director of state-run oil firm NNPC, told reporters at the damaged dock. "This is the first time this type of incident has happened."



BOLDER ATTACKS

MEND has rarely attacked sites outside the Niger Delta, focusing mainly on oil facilities in Delta, Bayelsa and Rivers states in southern Nigeria.

"They are obviously getting much bolder," said a private security source working for the oil industry. "We are on the lookout for more attacks. They could happen anywhere now."

Analysts say the militant group may be trying to strengthen its position before possible talks with the government.

MEND, which is in the process of forming a negotiating team, said it would use a "two-pronged approach of combining dialogue and intensifying attacks throughout the course of negotiations."

The violence has already forced Royal Dutch Shell (RDSa.L), U.S. oil company Chevron (CVX.N) and Italy's Agip (ENI.MI) to shut down around 300,000 barrels per day of production in the last seven weeks, lifting global oil prices.

HENRY OKAH

The government met one of MEND's key demands by freeing Okah after more than a year in detention for suspected arms dealing.

President Umaru Yar'Adua ordered Okah's felony charges to be dropped after the rebel leader agreed to accept the government's "unconditional" amnesty.

"Having reviewed what the attorney general said, you have become a free man at this moment. You are now discharged," Judge Mohammed Liman told Okah at a hearing in the central city Jos.

The rebel leader is the first senior militant to participate in the federal amnesty programme, which Yar'Adua created last month in the hope of halting the unrest.

Some rebels have said they will lay down their arms after Okah's release, but analysts do not believe the violence will subside.

"I don't think the structure of the armed groups is such that you could have a simple settlement," said Antony Goldman, head of PM Consulting.

"The real issues in the delta are lack of cohesion, poverty, unemployment and environment damage. If it was easy, they would have resolved it long ago," he added. (Additional reporting by Hannington Osodo, Camillus Eboh, Felix Onuah and Matthew Tostevin in Johannesburg; Writing by Randy Fabi; editing by Tim Pearce)