Nigerian President Goodluck Jonathan is replacing the managing director of state oil company Nigerian National Petroleum Corp (NNPC) and three other senior directors on Tuesday, a presidency statement said.

"To further strengthen the ongoing reforms ... and in furtherance of efforts to achieve greater transparency and accountability ... President Jonathan has approved the re-composition of the executive management team of the NNPC," the statement said.

Jonathan has come under intense pressure to clean up Africa's biggest energy sector after public anger over corruption and waste of the country's oil wealth surfaced during January protests over fuel prices.

The incumbent Managing Director Austen Oniwon, the Finance and Accounts Director Michael Arokodare, Refining Director Philip Chukwu and Engineering Director Billy Agha have all been retired, the presidency statement said.

Oniwon will be replaced by Andrew Yakubu, a chemical engineer who has held several positions at NNPC, including executive director of exploration and production, the statement said.

Numerous reports and audits have said that corruption is rife within NNPC. Last year, Transparency International and Revenue Watch ranked NNPC as the least transparent oil company in the world.

Oniwon told Reuters in February that corruption in NNPC was "in the imagination of some people".

A parliamentary report in May uncovered a $6.8 billion fraud within the fuel subsidy, which is partly run by NNPC.

The report said NNPC was accountable to no one. It said the company owed the government 704 billion naira (US$4.33 billion) for subsidy violations and that it owed oil traders, including Trafigura, $3.5 billion in unpaid bills.