Twenty-one of the Chibok schoolgirls kidnapped by Boko Haram Islamic extremists more than two years ago have been freed in negotiations, officials said Thursday.
A Nigerian military source says four detained Boko Haram leaders have been freed in exchange for the release.
Some 197 girls remain captive, though it is not known how many of them may have died.
The freed girls, the first to be released as a result of government action, are in the custody of Nigeria's Department of State Services, Nigeria's secret intelligence agency, according to presidential spokesman Garba Shehu.
He said their release was negotiated between the government and Boko Haram in talks brokered by the International Committee of the Red Cross and the Swiss government. He said negotiations will continue for the release of the other students.
This Monday May 12, 2014 file image taken from video by Nigeria's Boko Haram terrorist network, shows the alleged missing girls abducted from the northeastern town of Chibok. (Photo: AP)
"We are extremely delighted and grateful,'' said the Bring Back Our Girls movement on Facebook. The group, which has campaigned within Nigeria and internationally for the release of the students, said it awaits the names of the released girls.
Boko Haram long has offered to free the girls in exchange for detained leaders of the group.
The ICRC in the past had tried to negotiate a swap, which failed. Information Minister Lai Mohammed said last month that negotiations last year ended when Boko Haram demanded a ransom of $5.2 billion for the girls' freedom.
The abduction of 276 schoolgirls in April 2014 and the government's failure to quickly free them has caused international outrage and brought Boko Haram, Nigeria's home-grown Islamic extremist group, to the world's attention. Dozens of the girls escaped on their own, but most remain missing.
People take part in a march that is part of the 'Bring Back Our Girls' campaign, in memory of the Nigerian girls abducted by Nigerian extremists, outside the presidential residence in Abuja, Nigeria, July 8, 2015. (Photo: AP)
In May, one of the girls, Amina Ali Nkeki, escaped on her own. Shortly after her release Nkeki told her family that some of the kidnapped girls died of illness and that others, like her, have been married to fighters and are pregnant or already have babies, her mother told the press.
Since then Nkeki has been in the custody of the secret service where she is receiving medical care and trauma counselling, according to President Muhammadu Buhari's government. The government has been criticized for keeping her isolated. The Bring Back Our Girls group and Human Rights Watch have asked whether Nkeki now is a detainee of the government.