"Holding your ground with honour is a thousand times easier than retreating in shame," he said in the message release early on Thursday morning by the Isil-affiliated Al-Furqan media.

"To all the people of Nineveh, especially the fighters, beware of any weakness in facing your enemy."

He called on Isil supporters to fight the "enemies of God" and for the suicide fighters to "turn the nights of the unbelievers into days, to wreck havoc in their land and make their blood flow as rivers."

It was widely reported last year after the air strike that the jihadist leader had suffered a bad spinal injury. Isil's top leadership apparently held talks about who would replace him.