A Christian schoolgirl abducted by Boko Haram is still being held hostage by jihadists because she refused to convert to Islam.

Leah Sharibu, 15, was among more than 100 schoolgirls abducted from their hostel in the town of Dapchi in the conflict-ridden northeast of Nigeria on February 19.

As the only Christian among the hostages, the teenager remains in captivity months after all the other girls were released.

The terrorists returned 110 Dapchi girls to the town on March 21, following negotiations with the government.

Schoolgirls who were released after being kidnapped in Dapchi in northeast Nigeria. But their schoolmate, Leah Sharibu, remains in captivity because she would not convert to Islam

Both the government and the jihadists claimed no ransom was paid, but a UN report this month said Nigeria paid huge sums for the girls' release.

Some of the released girls said five schoolmates died in captivity while Sharibu was retained for refusing to forsake Christianity for Islam.

In an unverified chilling recording Boko Haram sent to local media late yesterday, Sharibu begged Nigerian President Muhammadu Buhari to work for her freedom.

Her father Nathan Sharibu spoke of his joy at hearing her voice.

Sharibu said in her native Hausa, a language widely spoken in the north of the country: 'I plead with, the government and the president to have pity for me and save me from my situation.'

Sharibu faltered and repeated herself in the recording, suggesting she was reading from a prepared text.

If verified, it would be the first evidence that Sharibu was alive since she was kidnapped.

The audio was accompanied by a picture of Sharibu clad in a light brown hijab revealing only her face, sitting on a mat in an undisclosed location.

As the only Christian among the 100 hostages, Leah remains in captivity months after all the other girls were released

Buhari's spokesman Garba Shehu said on Twitter: 'The secret service is analysing the voice. Our reaction will follow the outcome of the investigation.

'For President Buhari, nothing will be spared in bringing all our girls home. He will not rest until all of them are freed.'

Nathan Sharibu, Leah's father confirmed the voice was his daughter and urged the authorities to secure her release when he told AFP today: 'The voice in the audio is no doubt that of Leah.

'As her father I can't mistake her voice. I'm delighted to have heard her voice because it proved beyond doubt that my daughter is still alive.

'The government has not contacted me to verify if the voice is indeed that of Leah.'

Fighters believed to be loyal to an IS-affiliated Boko Haram faction led by Abu Mus'ab Al-Barnawi abducted the girls after storming the Government Girls Science and Technical College in Dapchi in Yobe state.

The incident evoked memories of the April 2014 kidnapping of 276 schoolgirls from the town of Chibok in neighbouring Borno state.

Christian schoolgirl, Leah Sharibu, who was abducted by Boko Haram jihadists has called on President Muhammadu Buhari to secure her release in a chilling recording

Although more than 100 Chibok girls have been freed or rescued, some 112 are still missing.

Sharibu's case has stoked tensions among Christians, who have accused the government of failing to do enough to secure her release.

Nigeria is roughly evenly divided between Muslims and Christians and religious tensions lead to occasional flareups.

Sharibu's captivity has become a political issue with Buhari seeking a second term in office in February elections.