LAGOS - Nigerian militants said Monday they destroyed a Chevron oil pipeline junction in the latest attack on Nigeria's key money earner since the government offered an amnesty.

The Movement for the Emancipation of the Niger Delta (MEND) said it attacked the Okan manifold late Sunday.

According to the rebels, the manifold controls about 80 percent of the crude that Chevron Nigeria Limited sends to its BOP Crude Loading Platform.

A Chevron spokesman said an investigation had started and no comment would be made.

President Umaru Yar'Adua on June 25 offered an amnesty to any rebel in the Niger Delta, the main oil region, who lays down his arms.

The government has said the amnesty offer, which starts August 6, also applies to detained MEND leader Henry Okah.

But MEND, which says it is fighting for a fairer distribution of the Delta oil wealth, has claimed at least four attacks since the offer was made.

Its latest statement said: "As long as the Nigerian government and military JTF (Joint Task Force) has chosen to carry out kidnappings and arson against innocent communities and individuals, ... (we) will fight for them."

The group called for the release of a traditional ruler it said the military is holding.

It has also demanded the release of Okah, who was detained in September 2007 and now faces treason charges.

"Government should display the highest form of integrity and sincerity over the detention of Henry Okah at this period of his fading health," said the MEND statement.

MEND said on Saturday that it destroyed Shell's Cawthorn Channel 1 well head, which supplies the Anglo-Dutch company's key Bonny loading terminal in Rivers state.

On Saturday the rebels vowed to thwart a 10-billion-dollar trans-Saharan gas pipeline project linking vast reserves in Nigeria to Europe which has been agreed by Algeria, Niger and Nigeria.

No date has been given for the start of work on the pipeline which will be more than 4,000 kilometres (2,500 miles) long. But the first gas is scheduled to be delivered in 2015.

MEND urged oil firms still operating in the Niger Delta to leave immediately, threatening new attacks.

The group, which rose to prominence in December 2005, has targeted Shell, Chevron and Italian group Agip.

MEND is the strongest of a series of groups fighting in the Niger Delta since 2006. The unrest has reduced Nigeria's exports to 1.8 million barrels per day from 2.6 million three and a half years ago.