The Nigerian senate has launched an investigation into alleged financial mismanagement at the state-owned oil company.
This follows the leaking of a letter from Ibe Kachikwu, the state minister for oil, to President Muhammadu Buhari.
It accuses the managing director of the Nigerian National Petroleum Corporation, Maikanti Baru, of awarding contracts worth more than $26bn (£19.8bn) without due process.
There has been no word so far from Mr Baru. The NNPC’s spokesman said it was not possible to comment as the company had not received a copy of the letter.
Nigeria’s oil sector has been accused of corruption and mismanagement for decades.
