The government has promised to crackdown on unrest

Oil giant Shell has taken out full-page adverts in Nigerian newspapers warning of the "unimaginable carnage" that would result if one of its oil installations was blown up.

Shell said it had been warned that "criminal elements" were threatening to torch a storage vessel, putting production capacity of 170,000 barrels a day at risk.

"The scale of economic, human and environmental carnage that a blow-out on the FPSO (floating production, storage and offloading vessel) can result in is unimaginable," the advert warned.

"Information reaching us reveals that anytime from now, the vessel could be boarded by force of arms and set on fire," Shell wrote, adding that the forces were awaiting the signal to attack.

Anger over jobs

Oil firms working in Nigeria's delta region have been plagued by ethnic violence, repeated sabotage of pipelines and disrupted production.

The violence has come about because many people in the region are still living in poverty and have seen little benefit from the oil money.

The saboteurs are reportedly angry that they have not been offered jobs on the FPSO.

But Shell uses the advert to point out that people from neighbouring communities have been employed on the vessel and that the it is working to help improve the region's schools and infrastructure.

Damaging the economy

Newly re-elected President Olusegun Obasanjo has called for firm action by security forces to bring to an end to civil unrest in the oil-rich southern region.

Last month, oil firms including Shell and ChevronTexaco were forced to evacuate their staff and stop production during three weeks of violence.

Nigeria is the world's eight largest oil producer and relies on oil exports for more than 90% of its revenues.

The disruptions suffered so far this year are already likely to have dented the country's economic growth prospects, economists warn.

And the oil firms have been getting increasingly impatient with the situation, devoting their attention to offshore projects instead.