Nigeria's militant Islamist group Boko Haram has forced abducted women and girls to go to the front line to help fight the military, a new report says.
The group has taken more than 500 women and girls hostage since it began its insurgency in 2009, the Human Rights Watch (HRW) report adds.
Suspected militants seized about 30 children on Thursday, despite government claims of a truce.
Boko Haram has declared a caliphate in areas it controls in the north-east.
The group had intensified abductions since May 2013, when Nigeria's government imposed a state of emergency in the three states where Boko Haram was most active - Borno, Yobe and Adamawa, HRW said.
The HRW report comes as three girls who escaped Boko Haram after being abducted in April told their story to BBC Hausa.
In an animation of their story - at the top of this page - the girls describe their fear of being shot or hunted down by Boko Haram, and the dangerous journey back to safety.
'Shaking with horror'
The New-York based group estimates that more than 4,000 civilians have been killed in more than 192 attacks since May 2013 in the north-eastern and in the capital, Abuja.
At least 2,053 civilians were killed by Boko Haram in the first half of 2014, it says.
Who are Boko Haram?
- Founded in 2002
- Initially focused on opposing Western education - Boko Haram means "Western education is forbidden" in the Hausa language
- Launched military operations in 2009 to create Islamic state
- Thousands killed, mostly in north-eastern Nigeria - also attacked police and UN headquarters in capital, Abuja
- Some three million people affected
- Declared terrorist group by US in 2013
In the report, a 19-year-old woman says she was held in militant camps for three months last year.
In one operation, she was given a knife to kill one of five vigilantes captured by Boko Haram.
"I was shaking with horror and couldn't do it. The camp leader's wife took the knife and killed him," she said.
On another occasion, she was forced to accompany the men to the front line.
"I was told to hold the bullets and lie in the grass while they fought. They came to me for extra bullets as the fight continued during the day," the woman said.
"When security forces arrived at the scene and began to shoot at us, I fell down in fright. The insurgents dragged me along on the ground as they fled back to camp."
HRW said it had interviewed 30 women and girls who had either fled captivity or were released by Boko Haram.
They included 12 of the 57 who managed to escape when the militants raided a boarding school in the remote town of Chibok in Borno in April.
Boko Haram is still holding 219 of the girls it had abducted during the raid, sparking a global campaign for their release.
On 17 October, Nigeria's chief of defence staff said the military had agreed a truce with Boko Haram, and he was hopeful that the girls would be freed within a week.
However, Boko Haram has not commented on the alleged deal and the girls have not been released.
HRW said Boko Haram seemed to pick victims arbitrarily, though students and Christians were particularly targeted.
One young woman held in a camp described how combatants placed a noose around her neck and threatened her with death until she renounced her religion.
The women and girls interviewed said that some Boko Haram commanders appeared to make efforts to protect them from sexual violence.
However, HRW said it had documented eight cases of sexual violence perpetrated by fighters and most cases of rape occurred after the victims were forced to marry.
In the latest abductions, about 30 children were taken during Thursday's raid on Mafa village in Borno.
"The insurgents... grabbed young people, boys and girls, from our region," said Alhaji Shettima Maina, a local community leader for Mafa.
At least 17 people were also killed in the assault, blamed by the Nigerian authorities on bandits.