Believers are often singled out, tortured and faced with the brutal choice of converting to Islam or being slaughtered, according to Christian Freedom International.
Those who refuse to comply have reportedly had their limbs cut off or have been crucified.
Research by CFI found that more than 200 million followers are facing persecution in 105 countries making Christianity the most at-risk faith group in the world.
More Christians have been martyred in the 20th and 21st centuries than during the previous 19 combined, the organisation has claimed.
The human rights group’s president Jim Jacobson said: “Islamic State Militants in Iraq are using Christian churches as torture chambers where they force Christians to either convert to Islam or die.
“Islamic State militants are also stripping the former places of Christian worship of ancient relics which in turn are smuggled to Western collectors to help fund their terrorist activities.”
In August the terrorist group raided a Syrian church and abducted more than 230 Christians.
Days later they returned and bulldozed the 1,600-year-old monastery.
The extremists have abducted hundreds of Assyrian Christians from the war-torn country this year alone, many of whom were children and women.
In February, the hardline jihadists kidnapped at least 250 Assyrian Christians during a raid across ten villages in north-east Syria.
The militants released 19 of the hostages but the fate of the rest of those from the ancient Christian minority remains unknown.
According to Breitbart London, Mr Jacobson added: “I encourage you to pray for persecuted believers. They are your Christian family throughout the world.
“Pray for their safety; that they would be emboldened to continue sharing the Gospel even in the face of persecution; that their persecutors would also come to know Christ as they observe the courageous witness of these believers.”