"This change in work activity level, mainly in drilling and construction, is a precautionary measure that is being taken as a result of recent security incidents in the region," the company said in a statement.

Almost 40 gunmen on Tuesday attacked the DLB Cheyenne on six small boats and seized four of the company"s US subcontractors.

Chevron, the second largest US oil company, said the scaling down followed "increased challenges in the Niger Delta region" and was essential for "the safety and security of our workforce and facilities."

It would "have an impact on numerous contract workers," the statement added, but spokesman Michael Barrett declined to comment on the number of workers and subcontractors that would be affected.

"There is currently no immediate impact on production," the communique said.

Chevron said it is working with Nigerian government agencies and community leaders in the region to improve the security situation so it could resume normal business operations as soon as possible.

Last Monday, Chevron said it had temporarily shut down its Ebite flow station in southern Nigeria because of a community protest, affecting 42,000 barrels of crude per day.

A few days before six oil workers were taken hostage in a militant attack on one of Chevron"s floating storage vessels, causing the company to temporarily shut down 15,000 barrels per day from the Funiwa oilfield.

Chevron produces 360,000 barrels of crude per day in Nigeria according to its spokesmen here.

PIN/AFP