ISIS has threatened that three Christian women, whose photos have been leaked on social media, will be sold as sex slaves.

Three images of women holding signs with their names and a date were posted on social media last Friday, according to the Daily Mail.

These women could be among the large group ISIS kidnapped in February, when 220 Assyrian Christians disappeared from the province of Hassakeh in north-east Syria. A source from the Assyrian Federation of Sweden said, "the names resemble the family names of people in a nearby village...so it is possible that these women could be from Assyrian villages but we cannot confirm that."

The Federation fears the women could be sold as sex slaves to ISIS fighters if a ransom is not paid, although no amount is specified.

Last year ISIS released a 34-page manual making it clear that sex with Christians and Jews "captured in battle" was allowed. These groups have previously received limited protections above other communities such as the Yazidis because they are viewed as 'People of the Book.' However even this appears to have been removed as ISIS continues to systematically rape women and girls who do not hold to the group's radical Islamic theology.

An abducted 12-year-old girl was told by an ISIS fighter that because she wasn't a Muslim, the Qu'ran not only permitted her rape, it condoned and encouraged it, according to a recent New York Times interview.

There are fears that the already severe plight of Christians in Syria is worsening.

Last week ISIS kidnapped 230 Christians and Muslims from Qaryatain in Syria. Half were later released but the Syrian Observatory for Human Rights fears that the remaining hostages, at least 60 of whom are Christian, are bound for either death or slavery.