One of the missing Chibok girls has been found in Nigeria, the BBC has reported.

An activist told the BBC that a girl, Amina Ali, was found by a vigilante group on Tuesday in the Sambisa Forest, close to the Cameroonian border.

The 276 girls were abducted from their school in April 2014. Almost 50 of them managed to escape, but it is believed 219 remain in captivity.

This girl is the first of the 219 to be found since they were abducted more than two years ago.

The BBC reports that she was identified by a civilian fighter who recognised her.

Boko Haram, an Islamist militant group whose name translates as 'Western education is forbidden', has abducted hundreds of women and girls since its uprising in 2009.

Jihadists overran the school in Chibok, Borno state, late in the evening on April 14. All schools in Borno had been forced to close due to increased fighting, but the girls had returned to complete their exams.

Armed men killed a policeman and soldier who were guarding the school and then forced entry into the dormitories, ordering the students to climb into open-backed trucks. Some managed to escape, but two years on 219 are believed to remain in captivity.

Several weeks after the Chibok abduction, militants released footage of 136 of the schoolgirls purporting to show them having converted to Islam. The girls were shown wearing hijabs and reciting the Qur'an.

Nigerian authorities have faced overwhelming criticism for their failure to find the girls over the past two years. President Muhammadu Buhari, elected over former President Goodluck Jonathan last May, has pledged to fight Boko Haram's brutal insurgency and made security a key pillar of his campaign. However, despite the Chibok case being brought to international attention through the #bringbackourgirls campaign and a number of false rumours of their release, the girls remain missing.

Boko Haram has since abducted around 2,000 children, including some 300 in a November 2014 attack in Damasak. A report released this week by UNICEF said incidents of Boko Haram child suicide bombings have increased rapidly over the last year. Children as young as eight, the majority of them girls, have been used to bomb schools and markets.

Some reports suggest that at least some of the girls have been brainwashed by their captors, and have carried out murders on behalf of the group.