Nigeria's President Muhammadu Buhari is extending his stay in the UK as he needs more time to rest, his spokesperson has said. Buhari, 74, has been on medical leave in London for more than four weeks.

"During his normal annual checkup, tests showed he needed a longer period of rest, necessitating the president staying longer than originally planned," Adesina said in a statement. He added there was no reason to worry over the health of the head of state.

"Buhari thanks millions of Nigerians who have been sending good wishes and praying for his health and well-being in mosques and churches throughout the country," Adesina continued. "The president is immensely grateful for the prayers, show of love and concern."

It is not clear yet when Buhari is to return to Nigeria. Staff at Abuja House in west London refused to provide any updates on Buhari's health when IBTimes UK arrived at the government-owned building to find out more about his progress.

Is Buhari ill?

Nigerians have become increasingly concerned with Buhari's health. The leader was scheduled to return to Nigeria on 6 February, but prolonged his stay to complete medical tests recommended by doctors.

The move fanned further rumours about his deteriorating health and is likely to erode confidence in his administration.

The Nigerian presidency has released several statements dismissing allegations Buhari was gravely ill or even dead.

Nigerians have also expressed disbelief following news that Buhari had a phone conversation with his American counterpart Donald Trump.

Adesina, who confirmed the phone call took place, described the conversation – the first since Trump assumed office in January – as "cordial". The US government also confirmed the phone call took place, but no details of the conversation were given.

People have drawn similarities between Buhari's medical leave and that of deceased former president Umaru Yar'Adua, who was admitted to a hospital in Saudi Arabia in 2009.

The country experienced a power vacuum filled only when the senate approved a Doctrine of Necessity to allow the then vice-president Goodluck Jonathan to be sworn in.

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