Abuja - Nigerian state governors are to look into why potentially billions of dollars in oil revenue were allegedly not paid into government coffers, as part of a wider probe into the state-run oil firm.
A four-man panel will seek answers from the Nigerian National Petroleum Corporation (NNPC) about apparent discrepancies in its accounts, as well as alleged plundering from a reserve account.
President Muhammadu Buhari last week dismissed the entire board of the NNPC, which is widely seen as riddled with corruption, and has given his approval for the governors' investigation.
The governor of southern Edo state, Adams Oshiomhole, told reporters in Abuja on Monday evening the panel will look at NNPC accounts on crude oil sales between 2012 and May this year.
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"The NNPC claimed to have earned 8.1 trillion naira ($40 billion, 36 billion euros), what NNPC paid into the Federation Account... was 4.3 trillion naira," he said.
"What it means is that NNPC withheld and spent 3.8 trillion naira... That tells you how much is missing, what is mismanaged, what is stolen. There are huge figures," he alleged.
The governor of the Central Bank of Nigeria, Lamido Sanusi, last year claimed $20 billion in oil revenue had not been remitted from 2012 to 2014.
The government of former president Goodluck Jonathan disputed the figures and in the political row that followed, Sanusi was dismissed.
Oshiomhole said the panel would also look into a massive dip in Nigeria's excess crude account, into which the difference between government-set oil prices and the international rate is deposited.
He said the account has plunged to $2 billion from $4.1 billion in November 2014.
Buhari took office on May 29 after defeating Jonathan in elections in March.
He has vowed to tackle corruption and particularly the rot in the oil sector, which provides Nigeria -- Africa's biggest crude producer -- with the majority of government revenue.
A slump in global oil prices since mid-2014 has squeezed Nigeria's economy, forcing government projects to be put on hold or scrapped and led to a review of this year's budget.
Many public sector workers have not been paid for months and last week Buhari said Jonathan's administration had left the treasury "virtually empty".
Buhari has been advised to overhaul the NNPC and scrap a scheme that ensures cheap fuel at the pumps but pays importers and suppliers the difference in the market rate.