Nigeria's central bank governor Olayemi Cardoso said on Friday that entities involved in fraudulent foreign exchange trades would be punished, after an audit helped whittle down a backlog of claims for payment to a "more manageable figure."

A forensic audit of $7 billion of overdue forex backlogs the bank has been struggling to clear had uncovered irregularities affecting $2.4 billion worth of the transactions.

The irregularities ranged from missing paperwork to non-existent entities and beneficiaries receiving unauthorised foreign exchange allocations.

"A lot has been asked with respect to those that are within the infracted category, which we are looking at very closely. Those who are responsible will be sanctioned accordingly," Cardoso told lawmakers on Friday at a parliamentary hearing.

Africa's largest economy is experiencing a crippling dollar shortage that has pushed its currency to record lows in recent weeks, though Cardoso said on Tuesday that dollar liquidity has started to improve.

Central bank Deputy Governor Muhammad Sani Abdullahi, also at the hearing, added that the bank is working with law enforcement for further action against the offenders.

So far, about $2.5 billion of the backlog across sectors such as aviation, energy and manufacturing has been paid, leaving a balance of $2.2 billion.

Cardoso said the bank had already moved towards settling a substantial number of outstanding forex backlogs. He did not elaborate.

(Reporting by Elisha Bala-Gbogbo, Editing by William Maclean)