The measures, according to four banking and regulatory sources, will be fines against Citibank, Standard Chartered PLC, Diamond Bank PLC and Stanbic IBTC Bank PLC for their role in MTN's repatriation of billions of dollars the firm held in Nigeria and sent out of the country.

Nigeria's central bank will also ask MTN to return money it improperly repatriated, said a person at the firm familiar with the matter and a banking source, speaking on condition of anonymity.

(Reporting by Camillus Eboh and Chijioke Ohuocha)