The Nigerian air force says it carried out strikes on illegal oil refining sites in the Niger Delta region on Sunday.

The force said it had destroyed several illegal sites in oil-rich Rivers state and also targeted a boat that was loaded with crude oil and headed for the open waters.

Nigeria has been cracking down on oil thieves in the Niger Delta, burning crude-laden ships and small illegal refineries, but aerial bombardments are uncommon.

Most of the illegal oil refineries tend to be located in the creeks away from communities but environmentalists have condemned the continual burning of the refineries.

Illegal crude vessels that have been seized in the past by a private security contractor have also been burned by authorities, with the crude intact.

Sunday's attacks coincided with a visit of defence and oils chiefs to Rivers state, where Nigeria’s National Security Adviser Nuhu Ribadu said the country was losing 400,000 barrels of crude daily to thieves.