Nigeria's President Goodluck Jonathan has ordered a forensic audit of the state oil firm following claims that $20bn (£12bn) had gone missing.
Suspended central bank governor Lamido Sanusi caused shockwaves last month when he said that $20bn in oil revenue had not been accounted for.
Mr Jonathan's office denied the claim and said "reputable international firms" would carry out the audit.
Nigeria is one of the world's biggest oil producers.
However, many of its citizens still live in poverty and say they have not benefited from the country's oil wealth.
Nigeria's oil sector is seen as notoriously opaque and corrupt, correspondents say.
Mr Sanusi was suspended last month after he told a senate committee that the Nigeria National Petroleum Corporation (NNPC) had failed to account for $20bn of the $67bn of oil sold between January 2012 and July 2013.
The presidency said in a statement that Mr Sanusi's suspension had "absolutely nothing" to do with his "patently untrue" allegations.
"But government is making no effort to bury them as he falsely claims," the statement said, adding that foreign firms would carry out the audit.
Nigeria's Finance Minister Ngozi Okonjo-Iweala and the senate committee also called for an audit after Mr Sanusi presented his evidence to MPs.
Mr Sanusi has said he would challenge Mr Jonathan's decision to suspend him.
Mr Jonathan's office says he was suspended for unrelated "financial recklessness" and "gross misconduct" at the central bank.
The NNPC has denied the money is missing, saying the allegations showed "little understanding of the technicalities of the oil industry".
Mr Sanusi is widely respected in financial circles and was named central bank governor of the year for 2010 by Banker magazine.