U.S. oil giant Exxon Mobil's Nigerian subsidiary warned on Wednesday it may not meet production expectations following the shutdown of a pipeline after an oil spill off southern Akwa Ibom state.

Mobil Producing Nigeria declared "force majeure" and said it had "difficulty in meeting projected liftings because of repair work on a section of pipeline affected in a November 9 oil release incident."

Force majeure is a legal term releasing a company from contractual obligations owing to circumstances beyond its control. Exxon Mobil (IW 500/1) did not say when the measure would be lifted.

It said that it had notified appropriate regulatory agencies and clients.

Nigeria is Africa's biggest oil producer. Its oil-producing Niger Delta region has been badly contaminated by decades of spills.

Spills occur frequently in the region due to a range of factors, including sabotage by oil thieves or militants as well as operational or maintenance faults by the oil companies.

Militants claiming to be fighting for a fairer distribution of oil revenue have also regularly blown up pipelines in the past, though such attacks have greatly decreased since a 2009 amnesty deal.

 Copyright Agence France-Presse, 2012