Islamic State fighters have been targeting children as young as eight for rape by drawing their victim's names in a sick 'lottery'.

An horrific account of atrocities committed by Isis fighters against abducted Yazidi women and children has been released by the Human Rights Watch.

The study, which includes accounts of 20 women and girls who escaped from ISIS, shows a system of organised rape and sexual assault, sexual slavery and forced marriage – acts that constitute war crimes.

In one harrowing account, a 12-year-old girl, who escaped her captors, revealed she was tied up, beaten and raped by seven different IS militants after being kidnapped from her home in Yazidi.

The girl, who has been named "Jalila", to protect her real identity, described how she was abducted with seven members of her family, when Arab men stormed her village north of Sinjar in August 2014.

Several weeks later, she was separated from her family and taken to a house in Syria where other abducted Yazidi women and girls were held.

She described how she was selected by an ISIS fighter to be raped. "I told him not to touch me and begged him to let me go", she said. "I was a young girl, and I asked him, 'What do you want from me?' He spent three days having sex with me."

During her captivity Jalila was 'owned' by seven ISIS fighters and raped on multiple occasions.

Another woman, identified as Rashida revealed the sickening 'lottery' from which the victim's names were drawn.

"Later that day they made a lottery of our names and started to choose women by drawing out the names," the 31-year-old said. "'The man who selected me, Abu Ghufran, forced me to bathe but while I was in the bathroom I tried to kill myself. I had found some poison in the house, and took it with me to the bathroom. I knew it was toxic because of its smell.

"I distributed it to the rest of the girls and we each mixed some with water in the bathroom and drank it. None of us died but we all got sick."

Dilara revealed she was taken to a wedding hall in Syria where ISIS fighters would come to buy girls to rape them.

She said: "I saw in front of my eyes ISIS soldiers pulling hair, beating girls, and slamming the heads of anyone who resisted. They were like animals.... Once they took the girls out, they would rape them and bring them back to exchange for new girls. The girls' ages ranged from eight to 30 years... only 20 girls remained in the end."

The report concludes that the campaign of systematic rape and violence committed against women and children is tantamount to war crimes and crimes against humanity, violating the laws of war.

Survivors are urged to obtain the medical and psychological treatment they need to cope with trauma they have suffered and better support needs to be provided to victims.

Liesl Gerntholtz, the women's rights director at Human Rights Watch said: "Yazidi women and girls who escaped ISIS still face enormous challenges and continuing trauma from their experience. They need urgent help and support to recover their health and move on with their lives."