One of more than 200 schoolgirls abducted by Islamist militant group Boko Haram from their school in north-east Nigeria's Chibok in 2014 has been found by soldiers, a Nigerian army spokesman said on Saturday.

Around 270 girls, most of them Christians, were taken from their school on April 14, 2014. Dozens have managed to escape, but more than 200 are still missing.

Their capture was part of Boko Haram's seven-year-old insurgency to set up an Islamic state in the north of Nigeria that has killed some 15,000 people.

Spokesman Sani Usman said the girl was discovered by troops who were screening escapees from Boko Haram's base in the Sambisa forest on Saturday around 06:00 am (0500 GMT) in Pulka, Gwoza Local Government Area, in Borno State.

The girl, Maryam Ali Maiyanga, was "discovered to be carrying a 10-month-old son", the army spokesman said.

Last month, 21 of the abducted girls were released by Boko Haram following talks with the government brokered by the International Red Cross and the Swiss government.

The first of the schoolgirls to be found was discovered by soldiers on the edge of the Sambisa forest, a vast woodland area, in May.

More than 910 schools have been targeted by Boko Haram, whose name means "Western [or non-Islamic] education is a sin". At least 611 teachers have been deliberately killed and another 19,000 forced to flee. At least 1,500 schools have closed.

In a video released in May 2014, then-Boko Haram leader, Abubakar Shekau, said women and girls would continue to be abducted to "turn them to the path of true Islam" and ensure they did not attend school. 

Additional reporting by Reuters.