US President Donald Trump has congratulated his Nigerian counterpart for his "good work" and pledged more assistance to help in the fight against terrorism in Nigeria. Trump made the remarks on 13 February during a telephone conversation with Muhammadu Buhari, currently on a medical leave in London.

Buhari's spokesperson Femi Adesina described the conversation – the first since Trump assumed office in January – as "cordial".

The two heads of states discussed ways to fight terrorism in Nigeria, where more than 20,000 people have been killed by Boko Haram militants since 2009.

"Trump encouraged President Buhari to keep up the good work he is doing, and also commended him for the efforts made in rescuing 24 of the Chibok schoolgirls and the strides being taken by the Nigerian military," Adesina said in a statement, referring to the schoolgirls kidnapped by Boko Haram from the Chibok village, in the restive Borno state, in April 2014.

"Trump assured the Nigerian president of US readiness to cut a new deal in helping Nigeria in terms of military weapons to combat terrorism," Adesina continued. He then added that Trump invited Buhari to Washington.

The phone call occurred as Nigerians are become increasingly concerned with the health of their head of state, who was scheduled to return to Nigeria on 6 February.

However, Buhari prolonged his stay to complete medical tests recommended by doctors in a move that 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 after fake versions of news websites Metro UK and the Huffington Post reported that the leader had died and "was caught committing suicide".

On 9 February, the presidency posted on social media pictures of Buhari meeting senator Bola Ahmed Tinubu and Chief Bisi Akande at Abuja House, in London's Holland Park.

However, staff at the Abuja House 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.

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Who are Nigeria's Boko Haram?

Boko Haram, which has renamed itself ISWAP, fights against Western influence in Nigeria and aims to impose its version of Sharia law throughout occupied territories.

The group launches attacks in Nigeria and neighbouring countries in a bid to take control of more territory. Three Nigerian states – Adamawa, Borno and Yobe − have been under a state of emergency since May 2013.

Boko Haram has killed more than 20,000 people since 2009 and was deemed the world's deadliest terror group, surpassing Islamic State in November 2015. Nigeria has also become the world's third-most terrorised country as a result of the group's violent insurgency.