Nigeria's largest rebel group is warning oil workers to leave the Niger Delta region within 72 hours to avoid what the group threatened would be an "imminent attack."

The Movement for Emancipation of the Niger Delta issued the warning in a statement Saturday.

The group said it would target what it described as "greedy" contractors who are repairing oil pipelines that have already been destroyed.

MEND says it is fighting for some of the region's oil wealth to be distributed to the impoverished people of the southern Niger Delta.  The Nigerian government has said the rebels are criminals.

On Friday, the militants swiftly rejected a second amnesty offer from President Umaru Yar'Adua aimed at bringing an end to the rebels' violent campaign.

MEND responded to the offer by promising to continue attacks until the government corrects what the group called an "injustice" in the oil region.

Dozens of soldiers and militants have been killed in the last three weeks, after the army launched an offensive against the rebels.

Some information for this report was provided by AFP.