Nigeria's energy company says electricity output fell dramatically Friday following an attack on a natural gas plant operated by Royal Dutch Shell in the restive Niger Delta.

Nigerian officials say unknown attackers blew up the Utorugu pipeline which supplies gas to the state-owned Nigerian Gas Company to feed power stations in Africa's most populous nation. The facility is jointly owned by Shell Nigeria and the Nigerian Gas Company.

No group has claimed responsibility for the attack, but the spokesman for the military in the Niger Delta, the Joint Task Force, JTF, Colonel Rabe Abubakar, says security forces are doing whatever they can to stop further attacks on the oil industry.

"JTF is a professional body, composed of professional soldiers and officers who are patriotic, who are resilient in carrying out our assignment here, and we will keep on doing it mindless of the small pockets of saboteurs who are cowards, who tend to blend with the community people and cause all these havoc. Their days will soon be numbered and they will come to regret what they have done," he said.

Nigeria is a major exporter of oil and gas, but suffers from severe energy shortages which produce frequent electricity cuts. Power output remains at a fraction of the amount needed by a country of more than 140 million people.

The energy company says the attack has compounded Nigeria's energy crisis, slashing national power output from 2,400 megawatts to 1,400.

A committee set up by President Umaru Yar'Adua to review the sector says Nigeria needs $85 billion meet its domestic power demand, estimated at roughly 20,000 megawatts.

Analysts point out that the latest attack underscores the fragile nature of a ceasefire between militants and security forces in the Niger Delta. Militants and the army agreed to a ceasefire following a presidential amnesty offer. The government has asked all militants and criminals to hand over their weapons by October or face tough action.