Displaced people from the minority Yazidi sect, fleeing the violence in the Iraqi town of Sinjar, re-enter Iraq from Syria, Aug. 10, 2014. Islamic State group militants have killed hundreds of Iraq's minority Yazidis, burying some alive and taking women as slaves. Reuters

Girls and young women in Iraq captured by Islamic State group militants have been separated from their families, forced into marriages and sexually abused under a growing system of slavery, according to media reports. The practice suggests that the militant group also known as ISIS is seeking to carry out modern-day slavery at a time when forced labor, debt bondage, trafficking and forced marriages are on the rise internationally.

In October, ISIS justified its use of women as sex slaves in its online magazine with claims that taking the women of "infidels" was permitted under Sharia law. "One should remember that enslaving the families of the kuffar -- the infidels -- and taking their women as concubines is a firmly established aspect of the Shariah, or Islamic law," the missive read.

Middle East scholars, however, argue that Shariah law suggests slavery is unethical. "There is not one single verse suggesting that the practice should continue. Further, the Quran makes no mention of slave markets or slave trading, and it repeatedly exhorts believers to free their slaves as an exemplification of their piety and belief in God," wrote Bernard Freamon, a professor of human trafficking at Seton Hall University School of Law in New Jersey, who also specializes in Islamic Legal History, for CNN.

Many of the victims have been from the minority Yazidi religion, which has been under attack in northern Iraq for months by ISIS. The girls and young women who escaped have described the Islamic State's tactics, including regular beatings and sexual attacks. Islamic State group fighters posted a video last month on YouTube that described the buying and selling of Yazidi girls on “slave market day.” “Today is the day of (female) slaves and we should have our share,” a fighter declares, according to the New York Times.

Some of the girls are only 12 years old, Vice reported. "These women have been treated like cattle," Nazand Begikhani, an adviser to the Kurdistan Regional Government on gender issues, told CNN. "They have been subjected to physical and sexual violence, including systematic rape and sex slavery. They've been exposed in markets in Mosul and in Raqqa, Syria, carrying price tags."

ISIS' human trafficking comes as modern-day slavery increased by 20 percent from last year, according to a report released Monday by the anti-slavery campaign group Walk Free. It concludes that nearly 36 million people are enslaved this year, according to the BBC. India and China had the highest number of modern-day slaves.