In a speech at a conference in New York Sarkis Boghjalian, American director of Aid to the Church in Need, said IS was waging an "uncompromising war for religious cleansing".
Speaking at the Hudson Institute conference he urged the world to do more to tackle the 'genocide' of Christians in the Middle East.
Islamic State has taken over large parts of Iraq and Syria in a bid to create a caliphate ruled by a strict interpretation of Islamic law.
Mr Boghjalian said: "There is no doubt that the Middle East has been set on fire; while the international community is watching, Christians and other religious minorities suffer human rights violations and religious persecution of the worst kind."
He added: "The acts of ISIS show clear intent - violent and brutal executions targeting Christians and Yazidis who represent distinct "national, ethnic, racial and religious groups" in Iraq.
"The intent of ISIS goes beyond destruction; It aims to erase the past, present and future of the Christians and Yazidis."
He urged the world to do more to stop the terrorist group.
"For the Christians in the Middle East, fear and a sense of abandonment is among the greatest crosses they have to bear," he said.
"The world must respond. We must not allow the annihilation of Christianity in the Middle East."