Nigeria's president says he feels healthy enough to return home from medical leave in Britain and is awaiting his doctor's permission.

Muhammadu Buhari, 74, has been undergoing medical treatment for an undisclosed illness since early May.

The absences and lack of information have prompted numerous protests, including demands that Buhari should resign.

"I am okay," Buhari said, according to a statement by the information ministry on Saturday.

READ MORE: Nigerians tell absent Buhari - 'Resume or resign'

"I feel I could go home, but the doctors are in charge," he said.

There has been a "tremendous improvement" in his health, he said.

Photos released by the president's office show Buhari standing outdoors, smiling and wearing sunglasses while holding a large "get well soon" card - with a handful of officials around him - in a residential area.

Buhari's extended absence - his second this year - left many in Nigeria questioning whether he was well enough to run the country.

Further treatment

Some have called for Buhari's replacement, and the military has reminded its personnel to remain loyal.

Buhari has spent more time since the beginning of 2017 in Britain than in Nigeria.

He was in London from January to March for sick leave before returning to Britain in May for further treatment.

Both times, Buhari appointed his deputy, Yemi Osinbajo, to act in his stead.

The health of Buhari has been a sensitive issue since the death in office in 2010 of Umaru Musa Yar'Adua, which led to months of political turmoil.

During the 2015 election campaign, Buhari rejected opposition claims that he was seriously ill with prostate cancer and said that they were a smear to show him as unfit for office.