Nigeria's Buhari flies to UK to see doctor

President Muhammadu Buhari flew out of Nigeria on Tuesday, a source at the capital's airport said, less than a day after Buhari announced he was heading to Britain for medical reasons.

"I will be travelling to the United Kingdom tomorrow, to see my doctor, at his request," Buhari said on Twitter late Monday, a move that stoked fresh doubts about his health less than a year before presidential polls.

Buhari spent more than five months in London last year receiving treatment for an undisclosed illness.

He gave no details about the reason for the latest trip, but said he planned to be back in the capital Abuja on Saturday.

The 75-year-old former army general had stopped over in London to visit his doctor last week after meeting US President Donald Trump in Washington.

At the time, his spokesman Garba Shehu said health matters were not the reason for breaking the journey back from the United States.

But on Monday, Shehu said in a statement that Buhari did in fact visit his doctor then.

"In the course of the technical stop-over for aircraft maintenance in London on his way back from Washington last week, the president had a meeting with his doctor," said Shehu.

Buhari's government has been criticised for failing to update the public on his condition and repeatedly insisting the president was "hale and hearty" during the course of his illness.

Buhari said on his return to Nigeria from London last year that he "had never been so sick" and had undergone blood transfusions.

In seeking re-election in 2018, Buhari is defying calls from political heavyweights to step aside for a younger, more dynamic candidate.