The singer has branded the extremist militant network the greatest threat to global peace since World War II and he is certain military action to end the terror is inevitable.

More than five million refugees have fled Syria since I.S. fighters got a foothold in the country's bloody civil war, and Stewart argues swift action is needed to smash the organisation and bring the chance of peace to the region.

However, he fears U.S. politicians are wary of further military intervention because of public distaste at the human cost of the drawn-out operations in Afghanistan and Iraq.

Stewart tells British magazine Event, "I can't think of anything in the last 70 years that has been more scary than Islamic State. We're going to have to go in and fight them or else it's going to go on and on. Sooner or later we're going to have to face the music.

"But the public have got no taste for it, especially in America. They don't want to see any more boxes coming home with flags on the top."