Religious leaders say Isis persecution of Iraqi Christians has become genocide.

The Iraq-based leader of the Chaldean Catholic church, Patriarch Louis Sako, says Iraqi Christians face a 'human catastrophe'.

Isis's persecution of Iraqi Christians, which has already forced tens of thousands of men, women and children to flee for their lives, is fast becoming a genocide, religious leaders have warned.

Archbishop Athanasius Toma Dawod of the Syriac Orthodox church said that Isis's capture of Qaraqosh, Iraq's largest Christian city, had marked a turning point for Christians in the country.

"Now we consider it genocide – ethnic cleansing," he said. "They are killing our people in the name of Allah and telling people that anyone who kills a Christian will go straight to heaven: that is their message. They have burned churches; they have burned very old books. They have damaged our crosses and statues of the Virgin Mary. They are occupying our churches and converting them into mosques."