Dangote Group, controlled by billionaire Aliko Dangote, slammed a visit to its Lagos offices last week by Nigeria’s anti-graft commission and said the move was aimed at causing embarrassment.

“No accusations of wrongdoing” have been made against the company, it said in a statement released over the weekend after the Jan. 4 visit by officials of the Economic and Financial Crimes Commission in connection with a probe of the country’s central bank.

It said the incident was “designed to cause us unwarranted embarrassment,” adding that “at present, we are only responding to a request for information to assist the EFCC with their ongoing investigation.”

Officials at the EFCC have yet to release a public statement regarding the visit.

The investigation is part of a wider probe into the tenure of Godwin Emefiele, the former head of Nigeria’s central bank. The investigation was opened in July on the orders of President Bola Tinubu, who used his first speech after taking office in May to criticize a complex foreign exchange policy overseen by Emefiele.

The president said the practice encouraged arbitrage rather than “meaningful investment” in the economy. He suspended Emefiele in June and the former central bank chief was arrested shortly afterward and taken into custody. He was released on bail last month.

The investigation has accused Emefiele of manipulating the naira and also setting up hundreds of unauthorized offshore bank accounts, including one in the UK that alone contained 543 million pounds ($690 million). He has denied the allegations.

From 2015 until it was scrapped in June, the central bank under Emefiele attempted to shore up the official value of the naira by limiting the amount of dollars available from official sources. This opened a significant gap between the official and much weaker unoffical rate.

Firms able to get dollars at the official rate could profit enormously from this mismatch by a so-called round trip, where they converted dollars into naira at a rate that offered 70% or more in local currency.