Officials from the Nigerian anti-graft agency, the Economic and Financial Crimes Commission (EFCC), conducted a visit to the offices of Dangote Industries Ltd, owned by billionaire Aliko Dangote.

The visit is part of an ongoing investigation into Godwin Emefiele, the former head of Nigeria's central bank.

The EFCC is examining foreign exchange dealings with the central bank during Emefiele's tenure. Emefiele, who was arrested in June on charges including fraud, has denied any wrongdoing.

The investigation alleges unauthorised offshore bank accounts, including one in the UK with £543 million ($690 million), and accuses Emefiele of manipulating the naira.

Dangote Industries Ltd. officials have not responded to requests for comment.

Under Godwin Emefiele's leadership from 2015 until its discontinuation in June, the Nigerian central bank operated a complex foreign exchange regime.

The system aimed to strengthen the naira by restricting the availability of dollars from official sources, creating a disparity between the official and parallel markets.

President Bola Tinubu, who took office in May, criticised the policy for encouraging arbitrage in his inaugural speech.

The arrangement allowed entities obtaining dollars at the official rate to profit significantly through a "round trip" by converting into naira at a rate providing a 70% or higher return in local currency.

President Tinubu suspended Emefiele in June, leading to the former central bank chief's subsequent arrest and release on bail last month.