The U.S. representative to the anti-Islamic State coalition says morale inside the extremist group is plummeting as the forces arrayed against it are gaining momentum.

During congressional testimony Tuesday, Special Presidential Envoy Brett McGurk says the Islamic State's days in Mosul, Iraq's second largest city, are "numbered."

The Islamic State remains firmly in control of Mosul, which was once home to a million people.

Iraqi leaders have pledged to liberate Mosul this year. But McGurk says the U.S. won't put a timeline on the Mosul operation.

McGurk's testimony comes two weeks after a lone gunman who pledged solidarity with the Islamic State killed 49 people and injured 53 at an Orlando nightclub.

McGurk says no direct link has been found between the Orlando gunman and the Islamic State.