Ethnic Ijaw militants launched a violent uprising last month to protest what they said was their marginalisation in the run-up to the recent Nigerian polls, forcing three oil majors to evacuate wells in the western Delta.

At the height of the protests, Africa's largest oil producer had lost more than 40 percent of its daily exports, sending tremors through an oil market already nervous about the war in Iraq.

On Saturday, when much of Nigeria went to the polls, there was no voting in the Ijaw areas of the western Delta, where youths had burned electoral offices and police stations in protest against the election.

But on Thursday the two main firms operating in the western Delta -- US giant ChevronTexaco and Anglo-Dutch group Shell -- said they had slowly brought production back to more than two-thirds of its former level.

"As at Wednesday, we were producing around 260,000 barrels per day out of the 370,000 we lost during the unrest," a Shell official, who asked not to be named, told AFP.

A ChevronTexaco official told AFP that it is currently producing 310,000 barrels per day, down from 440,000 before the crisis, and that it was hoping to fully resume production soon.

No-one was available for comment from the third company that evacuated its facilities in the western Delta, France's TotalFinaElf.

Nigeria is the world's sixth largest oil exporter, with an OPEC quota of 2.018 million barrels per day, and a main source of oil for the United States, which refines its light, low-sulphur crude into petrol for cars.

On Thursday a spokesman for the Nigerian navy said that two former World War II US navy warships, which have since been refitted and used by the US Coastguard, had been deployed to the swamps of western Delta.

"Two ships are in Warri to protect oil installations and to prevent new violence in the area," navy spokesman Sinebi Hungiapuko told AFP.

The arrival of the ships was condemned as a provocation by an Ijaw militant faction dubbing itself the Mein Butu Youths Vanguard.

"We will not accept intimidation or surrender, and are prepared to shed the last drop of our blood in our struggle for equity, fairness and justice within the Nigerian federation," said a statment from the group.

An AFP correspondent in the flashpoint city of Warri, 320 kilometresmiles) east of Lagos, said that naval personnel had sealed off a road leading to their wharf and deployed armed guards.

Although the navy has long claimed to have returned order to the area, on April 12 during a parliamentary election, a gunbattle broke out opposite the navy wharf in the rivers leading towards Ijaw villages.

Last month hundreds of troops and naval personnel were poured into the area after clashes in which eight servicemen, five oil workers and perhaps scores of villagers were killed. A tense stand-off developed.

Armed Ijaw militants targeted the neighbouring Itsekiri community, accusing them of conspiring with the navy and the oil majors to drive the Ijaw from the swamp and deny them access to oil money.

ChevronTexaco airlifted more than 3,000 Itsekiri refugees who had sought refuge in its Escravos tankfarm out of the swamps, and from the burned and devastated remains of their villages were left largely abandoned.

Earlier this month, a US defence official told AFP the ships, rebaptised the Kyanwa and the Ologbo by the Nigerian Navy, were 180-foot (60-metre) vessels whose 42-strong Nigerian crews were trained in the United States.

The seven ships are to be refitted at a cost to the US taxpayer of 750,000 dollars apiece before being donated to Nigeria.

SPACE.WIRE