Nigeria’s state oil company has offered to talk to an international watchdog that says it failed to hand over billions of dollars in oil revenues despite government promises to tackle mismanagement and corruption.

President Muhammadu Buhari last year fired senior staff at the Nigerian National Petroleum Corporation and approved a revamp of its structure last month.

But in a report published this week, the Natural Resource Governance Institute (NRGI) said NNPC withheld around two thirds of the $6.3 billion of oil proceeds in the second half of 2015.

The NNPC has previously said such accusations failed to account for its costs.

The oil sector in Nigeria, Africa’s top crude producer, accounts for about 70 percent of national income. (TVC)