Some of the Nigerian schoolgirls kidnapped by Boko Haram have been brainwashed and forced to kill other prisoners, the terror group's former captives said.

Three former women captives told BBC Panorama that some of the abducted schoolgirls have been brainwashed and convinced to carry out killings on the behalf of Boko Haram. The women claimed that they were held in same camps as some schoolgirls.

"They shared the girls out as teachers to teach different groups of women and girls to recite the Koran," a former captive, Anna, told the program, according to Independent. "People were tied and laid down and the girls took it from there. The Chibok girls slit their throats," she said.

Seventeen-year-old Miriam, a former captive of Boko Haram, said she was forced to marry a militant and is now pregnant with his child, according to Express.

"They told to us get ready, that they were going to marry us off. They came back with four men, they slit their throats in front of us. They then said that this will happen to any girl that refuses to get married," Miriam, who was repeatedly raped and now pregnant, told BBC Panorama. "There was so much pain.I was only there in body... I couldn't do anything about it," she said.

Amnesty International also said that a number of the abducted Chibok schoolgirls were now killing for Boko Haram. "The abduction and brutalisation of young women and girls seems to be part of the modus operandi of Boko Haram," said Netsanet Belay, Africa director of Amnesty International, according to The Guardian.

More than 200 school girls from Nigerian town of Chibok were kidnapped last year by Boko Haram fighters and most of them remained in the jihadist group's custody, according to Leadership Nigeria.