The Vatican has appealed to Muslim leaders to "unambiguously denounce and condemn" the barbaric practices of the Islamic State against Christians and Yazidis in Iraq, suggesting that their credibility may be damaged if they do not do so.

The Pontifical Council for Interreligious Dialogues, the Vatican department which deals with the Muslims, said that the massacre of Christians and Yazidis - an ancient and reclusive Zoroastrian religion that dates back to the Mesopotamian age - cannot be justified by any religion and "brings shame on humanity".

Among the crimes denounced by the Vatican are "unspeakable acts" such as beheading, crucifying and hanging bodies in public places; the forced expulsion of tens of thousands of people; the abduction of girls and women as spoils of war; the imposition of the barbaric practice of infibulation and the destruction of places of worship and Christian and Muslim burial places.

In the strongest condemnation yet of Islamic State practice, the Vatican statement said: "All must be unanimous in condemning unequivocally these crimes and in denouncing the use of religion to justify them. If not, what credibility will religions, their followers and their leaders have? What credibility can the interreligious dialogue that we have patiently pursued over recent years have?"

It also openly asks Muslim leaders to take a "clear and courageous stance" in denouncing the jihadists and "the invoking of religion to justify" crimes against humanity.

Pope Francis has been vocal in cricitising attacks against Christians after 100,000 of them were reported to have fled their homes in Iraq because of the Sunni militants' threat. Cardinal Fernando Filoni, a personal envoy of the Argentinian Pope, was sent to the region to show solidarity with the victims, provide them with emergency funding and meet Iraqi and Kurdish leaders.