Mr Adesina has denied all the allegations and was cleared of wrongdoing by an internal investigation, but US Treasury Secretary Steve Mnuchin has called for independent investigations.

The Nigerian banker, a former agriculture minister, will seek a second term at the bank's annual general meeting in August.

He visited President Buhari in the capital, Abuja, on Tuesday.

Mr Buhari said in a tweet that "Nigeria stands solidly behind Dr Akinwumi Adesina in his re-election".