A nine-year-old girl enslaved by the Islamic State (IS) is allegedly pregnant after being raped by her captors.

Aid workers reported that the girl was sexually assaulted by 10 men, and was one of hundreds of Yazidis recently released from captivity.

The prisoners were captured in June 2014 near Sinjar, and released near Kirkuk, Iraq last week. There were about 216 freed captives, mostly women, children, and elderly Yazidis.

An aid worker from Canada said that the women and girls were used as sex slaves for the militants.

"Most of them were front-line fighters or suicide bombers who are given girls as a reward," Yousif Daoud told the Toronto Star.

"This girl is so young she could die if she delivers a baby," he explained. "Even a caesarian section is dangerous. The abuse she has suffered left her mentally and physically traumatised."

The girl was taken to a hospital in Germany by a Kurdish charity.

The religious minorities have been driven from their homes, sold into slavery, tortured, and otherwise persecuted by IS in villages across northern Iraq. Tens of thousands were kidnapped last summer alone. Those freed last week reportedly displayed evidence of abuse and neglect, and were treated by Kurdish soldiers. Peshmerga commander General Hiwa Abdullah said that about 40 children were among those released, and many were exhausted and disoriented from their traumatic experience.

The Yazidis believed they were loaded onto minibuses to be executed and it is unclear why the prisoners were released. They reported being held in the IS-controlled city of Tel Afar before being shuttled from town to town in recent days.

A report issued by Amnesty International in December said that kidnapped Yazidi girls have committed suicide to avoid rape and forced marriage at the hands of IS.