Militants are using the places of worship as jails for those who refuse orders.
I.S. has been taking over large parts of Iraq and Syria whilst persecuting thousands of Christians and forcing most of them to leave the area.
The Fides news agency says the Chaldean church of the Immaculate Conception in Mosul is being used as a prison where men are taken blindfolded and handcuffed.
Whilst it's thought St. George's monastery is being used as a woman's jail. It's feared females being held in the church are facing sexual abuse by the Islamic militants.
There are now concerns that the churches could become legitimate targets for US led air strikes to tackle the fighters.