Islamic State is starting to sell captured women on social media as "sex slaves", according to new reports.

The Washington Post reports that an IS fighter Abu Assad Almani, believed to be a German man who has joined the terror group in Syria, advertised a young woman for sale at $8000 on Facebook.

Almani wrote on May 20: "To all the bros thinking about buying a slave, this one is $8,000." He also posted a different image of a pale woman, adding: "Another sabiyah [slave], also about $8,000. Yay, or nay?"

Facebook acted quickly to delete the account and the photograph but it was verified by Memri.

The Washington Post reports IS fighters have recently posted details on social media about buying and selling sex slaves, and discussed issues such as whether it is acceptable to have sex with prepubescent children - the answer given is "yes" - and the rules around beating slaves.

Steven Stalinsky, of Memri, told the Washington Post: "We have seen a great deal of brutality, but the content that ISIS has been disseminating over the past two years has surpassed it all for sheer evil. Sales of slave girls on social media is just one more example of this."

The photograph did generate some debate from the terrorist's friends, but not over the morality of posting it. 

They were more concerned to find out whether she was worth the asking price.

"What makes her worth that price? Does she have an exceptional skill?" asked one. 

According to Human Rights Watch (HRW), as many as 2000 women and girls, mostly Yazidi, are being held as sex slaves by IS, which has defended the practice as Islamic.

HRW has catalogued terrible abuses perpetrated against these women. The charity recently reported the case of Sari, who lost her son aged 12 and daughter aged 10 to IS and was then taken with her two younger children to a farm and ordered to convert to Islam where she was bought by a Saudi Arabian IS fighter called Abu Aris al-Tusi.

She was then sold three more times, each time by a man who raped her. One beat her children. She finally got away after her family found her on the internet, where her owner had advertised her for sale. He had made her wear make-up for the photograph. Her family paid him for her return.

According to ZeroHedge, the financial stress IS is operating under means the terror group now pays a substantial bonus to fighters who own a sex slave.