Nairobi/Abuja  - Nigerian President Umaru Yar'Adua has asked the nation's state-run oil company to demand around two billion dollars in arrears from oil companies Royal Dutch Shell and ExxonMobil, the BBC reported on Wednesday.

The government says that the two companies owe the money in unpaid taxes and production-sharing costs on two offshore oil fields.

ExxonMobil says it has complied with all legislation, while Shell refused to comment as it was still in discussion with the government.

Production in the oil-rich Niger Delta has been hit by regular attacks by militants on pipelines and production facilities. (dpa)