An Islamic State group spokesman has urged sympathizers in Europe and the U.S. to launch attacks on civilians there if they are unable to travel to the group's self-declared Caliphate in Syria and Iraq.

In a 31-minute audio message released late Saturday by the IS media arm al-Furqan, Abu Mohammed al-Adnani says the U.S.-led war against the group is doomed to failure and that America "fell in the swamp of perdition."

He tells IS sympathizers in Europe and the U.S. to "harass the Crusaders day and night and to terrify them until each neighbor becomes afraid of the other."

Adnani says sympathizers should not underestimate the value of "throwing a rock at a Crusader in the heart of his home."