Nigeria's President Muhammadu Buhari is seeking to extend his two-week 'medical leave' in the UK, his office has said.

The President, 74, was due to return to Nigeria on Monday but has requested to extend his leave for an unspecified time to await the test results.

His office said in a statement: "President Muhammadu Buhari has written to the National Assembly... informing of his desire to extend his leave in order to complete and receive the results of a series of tests recommended by his doctors."

His request has deepened suspicions that his health is worse than officials are publicly admitting.

However, his office have dismissed rumours that he is gravely ill, urging Nigerians to disregard "false and subversive messages" about the President's wellbeing.

It is the second time the President has travelled to the UK for medical treatment in a year.

In June last year, he flew to the UK for 10 days to receive treatment for a persistent ear infection.

The trip prompted criticism from leading doctor, Osahon Enabulele, former president of the Nigerian Medical Association for apparently reneging on a pledge to end medical tourism.