Nigerian militants killed four soldiers and one policeman in an unsuccessful attempt to capture a fuel tanker in the southern delta.
The militants, who are holding three foreign hostages, said they killed seven soldiers in a 45-minute firefight with troops last night, but a Navy spokesman said only four soldiers and one policeman died.
"There was an attempt by militants to seize the tanker and there was an exchange of fire. They are probably running out of fuel in their camps," the spokesman said.
The militants, who say they are fighting for more local control over the delta's oil resources, had earlier described the firefight as an attack by the army on their patrol boats in the Escravos River area of the vast wetlands region.
It was the latest in a series of confrontations between troops and the Movement for the Emancipation of the Niger Delta, whose attacks on the oil industry have cut oil exports from the leading OPEC nation by a fifth.
An army spokesman said the tanker was carrying refined fuel and was due to berth at Warri in the southern Delta state, where the state oil company has a refinery.
The militants released six hostages last week, but are still holding two Americans and one Briton taken during a series of attacks on Feb 18. which forced Royal Dutch Shell to shut 455,000 barrels a day, or one fifth of Nigerian output.