Chibok girls 'forced to join Nigeria's Boko Haram'

Some of the Chibok schoolgirls kidnapped in Nigeria have been forced to join Islamist militant group Boko Haram, the BBC has been told.

Witnesses say some are now being used to terrorise other captives, and are even carrying out killings themselves.

The testimony cannot be verified but Amnesty International says other girls kidnapped by Boko Haram have been forced to fight.

Boko Haram has killed some 5,500 civilians in Nigeria since 2014.

Two-hundred-and-nineteen schoolgirls from Chibok, are still missing, more than a year after they were kidnapped from their school in northern Nigeria. Many of those seized are Christians.

Three women who claim they were held in the same camps as some of the Chibok girls have told the BBC's Panorama programme that some of them have been brainwashed and are now carrying out punishments on behalf of the militants.

Seventeen-year-old Miriam (not her real name) fled Boko Haram after being held for six months. She was forced to marry a militant, and is now pregnant with his child.

Recounting her first days in the camp she said: "They told to us get ready, that they were going to marry us off."

She and four others refused.

"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,"

Faced with that choice, she agreed to marry, and was then repeatedly raped.

"There was so much pain," she said. "I was only there in body… I couldn't do anything about it."

While in captivity, Miriam described meeting some of the Chibok schoolgirls. She said they were kept in a separate house to the other captives.

They told us: 'You women should learn from your husbands because they are giving their blood for the cause. We must also go to war for Allah.'"

She said the girls had been "brainwashed" and that she had witnessed some of them kill several men in her village.

"They were Christian men. They [the Boko Haram fighters] forced the Christians to lie down. Then the girls cut their throats."

It is not possible to independently verify Miriam's claims. But human rights group Amnesty International said their research also shows that some girls abducted by Boko Haram have been trained to fight.