He told Associated Press that Isil is believed to have already moved its highest-trained bomb-makers out of Mosul and into Syria and southern Turkey.

He said: "They place a very high value on technical capacity and they will do everything they can to preserve it.”

Iraq witnesses almost-daily attacks that have been frequently claimed by IS, including Baghdad where multiple attacks took place Wednesday.

Iraqi forces have been met stiff resistance in Mosul, including waves of suicide car bombs, since launching an offensive to retake the city in October. They have retaken less than a quarter of the city since the operation began and coalition commanders expect fighting to last into the spring