The withdrawal began hours after armed militants stormed an oil facility operated by France's Total in the delta's Rivers state, killing three police officers.

Shell's pullout involves about 400 foreign family members from residential compounds in Port Harcourt, Warri and Bonny Island.

Staff will stay put and oil and gas production will not be affected, officials said.

"We are not sure if this thing is going to deteriorate.

If it deteriorates we will have fewer people to contend with," a senior Shell executive said.

Attacks on oil facilities and kidnappings of workers have become an almost a weekly occurrence in the world's eighth largest oil exporter.

But Monday's car bomb attack in the car park of a Shell residential compound in the region's largest city Port Harcourt brought the violence closer to home.

No one was killed or injured, but nine cars were damaged.

Despite the attack on the Total facility, oil production at the 35 000 barrel-a-day Obagi field in Rivers State was unaffected, a company source said.

Militancy and crime have risen dramatically this year in the vast wetlands region, which is home to all the OPEC member nation's oil and gas resources.

The mounting chaos is rooted in widespread poverty and decades of neglect by the Nigerian government, which has failed to convert the delta's oil wealth into local jobs or development.

Industry executives had been expecting security to decline before a landmark poll next April, because elections often reignite long-standing power struggles between rival clans and militias in the remote, lawless region.

Italian oil company Agip, a unit of ENI, has already transferred the families of its workers from the delta to Lagos.

Militants also detonated a car bomb at the perimeter fence of its Port Harcourt headquarters on Monday.

In February, Shell shut down its entire western delta operations after militant attacks and kidnappings, cutting Nigerian oil output by about a fifth.

Militants fighting for more control over the region's oil wealth are still holding four foreign oil workers, three Italians and one Lebanese, after an attack on an Agip oil export terminal on December 7.

It accused Agip of offering ransoms for the workers on Wednesday and vowed to kill the four men rather than free them for cash.

Criminal attacks against the industry are also common, often sponsored by local community chiefs seeking ransoms or other benefits from Western oil operators.

Unidentified gunmen are holding five Shell workers at a company base after invading the facility on December 14.

They argue the company owes the local community almost US$1 million.

Nampa-Reuters

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