Nigerian military officials say four soldiers and a policeman were killed in a fierce gun battle Wednesday with militants in the oil-rich Niger Delta.

A Navy spokesman said Thursday that the militants were trying to capture a fuel tanker on the Escravos River, but were repelled.  Officials say three militants were killed.

The militant group, the Movement for the Emancipation of the Niger Delta, says at least seven soldiers were killed during the gun battle.  They also say that army gunboats attacked them first.

The militants kidnapped nine foreign oil workers last month, but have freed six of them.  They say they will not release the other three until the people of the Delta region receive a greater share of oil revenues.

Nigeria is Africa's biggest oil exporter, but recent violence has forced an estimated 20 percent cut in the country's output.

Some information for this report was provided by AFP and Reuters.