The health of Nigeria's President Muhammadu Buhari has improved "significantly", a source within the Nigeria High Commission in London has said. Buhari, 74, is on medical leave in the UK, for the second time since the beginning of 2017.

Five things to know about Nigerian President Buhari's medical leave in UK

More from IBTimes UK

"He is doing very good; he is ok but his doctors will determine [when he will return]," the unnamed source told the Premium Times.

It is believed the source sees Buhari regularly. He spoke under condition of anonymity as he was not allowed to disclose details on the president's conditions.

Buhari spent nearly two months on medical leave in London earlier this year. He left again on 7 May, handing over powers to Vice President Yemi Osinbajo.

The head of state's medical trips, and mystery surrounding his medical condition, is sparking speculation about his health and the future of one of Africa's largest economies.

Analysts have previously warned Buhari's prolonged abscence could spark a power struggle ahead of the 2019 presidential elections, should the leader become incapacitated.

There have been calls for the president to step down, as some see him unable to continue to lead a country marred by corruption, economic recession and terrorism.

Commenting on resignation calls, the source at the embassy said: "That's the view of those arrogating God's power to themselves and would surely regret it, Insha Allah."

Is a coup d'etat likely to happen in Nigeria while President Buhari is in the UK?

After Buhari left Nigeria for the second time, rumours of a possible coup have spread.

Earlier this month, the army warned it had received information that "some individuals have been approaching some officers and soldiers for undisclosed political reasons". The Chief of Army Staff, Tukur Buratai, urged soldiers to abstain themselves from being involved in the country's politics.

On 24 May, the director of Defence Information, John Enenche, said in a statement that the army remained "totally loyal" to Buhari.

Analysts told IBTimes UK a coup is possible but unlikely. However, there are fears politicians loyal to Buhari, a Muslim from the north, could obstruct Osinbajo, a Christian from the south.

Nigeria up close: Check out our Flipboard magazine

Boko Haram