Militant action has severely cut Nigeria's oil output
Five people have been killed by Nigerian rebels who attacked an oil tanker facility, officials say.
Emergency crews said the bodies of five workers were found near the facility. They were all burnt beyond recognition.
The Movement for the Emancipation of the Niger Delta (Mend) said it had carried out the attack, near Lagos.
Meanwhile the leader of Mend, Henry Okah, has been released weeks after the government offered an amnesty to any rebel group willing to disarm.
But the Lagos attack marks a major escalation the activities of Mend, which has rarely attacked outside the Niger Delta.
The rebels say they are fighting for the rights of local people in the delta and for an increased share of Nigeria's vast oil wealth, but in the past the government has dismissed them as criminals.
The rebel attacks have severely reduced Nigeria's oil output. Production has been cut by one-fifth in the past three years, partly as a result of violence.
Emergency official Capt Geoffrey Boukoru told the AFP news agency attackers had exchanged fire with naval officers guarding the facility in Tarkwa Bay.
The jetty is the main entry point for ships entering Nigerian waters from the West and for oil tanker loading.
Capt Boukoru said the rebels were overpowered.
"In all five bodies were burnt beyond recognition, and they were all workers," he said.
In an statement Mend said "heavily armed" men had "carried out an unprecedented attack on the Atlas Cove Jetty in Lagos" at 2230 (2130 GMT) on Sunday.
Mend said its fighters had "injured or killed" at least nine navy personnel guarding the facility - though those claims have not been confirmed.
Capt Boukoru, said fire had damaged pipelines and forced the terminal to shut down for repairs.
Earlier, staff from the state-run oil firm NNPC told the BBC there had been a huge explosion followed by gunfire which lasted for about 30 minutes.
But they said there had been no loss of life.
The BBC's Caroline Duffield in Lagos says the timing of the attacks is significant, coming at a time when the government has offered an amnesty to the militants.
She says they are sending a message to the government - that they will continue to use violence at the same time as negotiations.
They hope to put pressure on the government to extract greater concessions as part of the amnesty. They want to show they have the capability to strike anywhere - even Lagos, the country's economic heart, our correspondent says.
The alleged attack follows claims by Mend in recent days that it had blown up several oil pipelines and captured six foreign crew from onboard an oil tanker.
The government recently offered an amnesty to members of any militant group that laid down its weapons - including Mend leader Mr Okah who had been facing treason and gun-running charges.
On Friday, lawyers for Mr Okah said he had accepted the amnesty offer.
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