ISIS is alleged to be carrying out 'systematic sexual crimes' against Yazidi women and girls after kidnapping over 200 of them from their homes in northern Iraq last August, Human Rights Watch (HRW) has said.
Those considered the most beautiful are then sent to Islamic State's adopted capital where they are sold naked, the UN envoy now claims.
They are first offered to the leaders of the depraved organisation, followed by the Emirs, and finally the soldiers.
Each buyer usually takes three or four girls and keeps them for a few months before they grow tired of them and sell them again, she told Middle East Eye.
She added: 'We heard of one girl who was traded 22 times, and of a Takfiri leader who had written his name on the girl's hand to show that she was his "property".
'Tens of thousands of the ISIS members expect that they will [get] women to [marry] following their recruitment.
She said the extremists banned the girls from using headscarves after some girls used them to hang themselves.
Bangura also claimed an abused young girl was burned alive after refusing to carry out 'extreme sexual acts'.
The city of Raqqa - where the girls are supposedly being taken and violated - was adopted by Islamic State as its capital city.
ISIS has released several gruesome images and videos from the city which show armed militants parading the streets, public executions and the extremists' all-female brigade which enforces its strict interpretation of Sharia Law.
But not all kidnapped girls are taken to the heart of Islamic State's brutal regime. In early April, more than 200 Yazidi women, children and elderly were released near Kirkuk after being taken hostage last June.
Aid workers reported that among them was a pregnant nine-year-old girl who suffered horrific sexual abuse at the hands of ISIS militants in northern Iraq. She claimed to have been 'sexually abused by no fewer than ten men'.
Hundreds of women and girls were also abducted by ISIS last year after the militants seized the Iraqi city of Sinjar which is mainly populated by Yazidi people.
And another Yazidi girl who was snatched from her family near Mosul described how ISIS stormed her town and took girls as young as ten to become sex slaves.
19-year-old Hanan told CNN she was regularly beaten and taken to a warehouse where hundreds of women were lined up and hand picked by the extremists.
There she met a fellow Yazidi girl who said she was held hostage, handcuffed and raped by ISIS fighters.
Women's Rights Director at HRW has claimed 'ISIS forces committed organized rape, sexual assault, and other horrific crimes against Yazidi women and girls.'
Liesl Gerntholtz added: 'Those fortunate enough to have escaped need to be treated for the unimaginable trauma they endured.'
