LAGOS: The main armed militant group in Nigeria on Saturday called off its unilateral ceasefire decreed last year in the country's vital oil-producing Niger Delta region and threatened new all-out attacks.

The Movement for the Emancipation of the Niger Delta (MEND) said in a statement emailed to reporters that it had taken the decision "after careful consideration and extensive consultation."

"This ceasefire was ordered in the hope that the government of Nigeria would consider true dialogue founded on a sincere desire to bring justice to the people of the Niger Delta, and true peace to Nigeria," it said.

The truce declared in October followed a government amnesty offer months earlier, but it was breached in December when the militants attacked a major pipeline operated by Shell and Chevron.

Before he was taken ill, Nigerian President Umaru Yar'Adua had last year launched peace overtures, offering the thousands of rebels an unconditional amnesty if they laid down their arms.

With promises of cash pay outs, re-training and re-integration into society, many of them did as MEND declared a ceasefire, in what was seen as the most credible efforts by a Nigerian administration to end the unrest in the volatile southern delta region.

However, several months on, the militants claim some of the promises are "preposterous," warning of serious renewed attacks on oil installations and workers.

"All companies related to the oil industry in the Niger Delta should prepare for an all-out onslaught against their installations and personnel," warned MEND.

"Nothing will be spared," it added.

"It is sufficiently clear at this point in time that the government of Nigeria has no intentions of considering the demands made by this group for the control of the resources and land of the Niger Delta to be reverted to the rightful owners, the people of the Niger Delta," the statement said.

Armed groups claiming to seek a greater share of oil revenue for locals have since 2006 staged audicious attacks on oil facilities in the Niger Delta and beyond, playing havoc with crude output and international oil prices.

At the peak of the attacks the violence slashed Nigeria's crude production by about one million barrels a day, which saw Angola outpace the west African giant as Africa's top oil producer

MEND warned all oil companies to halt operations as installations would be razed to the ground.

It threatened that the attacks would this time around extend to oil services firms which had "experienced a boom" from repairs of pipelines sabotaged in previous attacks.

Signs that the protracted uncertainty over the health of President Yar'Adua, hospitalised in Saudi Arabia for more than two months, would threaten to undo progress made towards peace in the restive region, started showing in recent days.

Top militant leaders Ateke Tom and Government Ekpemupolo early this week warned that Niger Delta youths see the "lull in the implementation of the promises as a betrayal" by government.

"Acting like a victor over a conquered people, the government rolled out a list of its plans for the Delta which it assumed would end decades of agitation, promising at the same time to deal with all who remained dissatisfied with its lame effort to re-dress the injustice in the Niger Delta," said MEND.

It accused the government of failing to repair roads and railway lines in the southern Niger Delta but considering using some of the oil resources to develop the north, home region of President Yar'Adua and where the country's dilapidated oil refineries are located.

"This government is hoping it can divide the people of the Delta in order to govern and plunder the Niger Delta," it said.

Nigeria is the world's 8th largest crude exporter. Oil is its economic mainstay, raking in some 95 percent of export earnings and accounting for about 85 percent of budget requirements for the OPEC member country.