Jihadists from Isil have in recent weeks boasted of wanting to extend their caliphate to Rome, the heart of Western Christendom, and have talked of planting the jihadist black flag on top of St Peter's Basilica.

Habeeb Al Sadr said there were also indications of a more specific threat against Pope Francis, who recently spoke out in favour of the US and its allies halting the advance of ISIS in Syria and Iraq.

"What has been declared by the self-declared Islamic State is clear – they want to kill the Pope. The threats against the Pope are credible," the ambassador told La Nazione, an Italian daily, on Tuesday.

"I believe they could try to kill him during one of his overseas trips or even in Rome. There are members of ISIS who are not Arabs but Canadian, American, French, British, also Italians.

"ISIS could engage any of these to commit a terrorist attack in Europe."

The ambassador said the Pope had made himself a target by speaking out against the human rights abuses committed against Christians in Syria and Iraq, as well as by his approval of attempts by the US to try to roll back ISIS.