Islamic State Struggling to Reinforce Mosul Ahead of Iraqi Offensive

The size of the force left to defend the Islamic State terror group's last stronghold in Iraq has been cut by as much as two-thirds with perhaps just weeks to go until Iraqi forces launch an all-out assault to recapture the city.

U.S. military officials said Thursday IS has only 3,000 to 4,500 fighters left in Mosul, describing the force as a mix of Iraqis and foreign fighters.

"They know they don't have what it takes to stop that offensive," Operation Inherent Resolve spokesman, Col. John Dorrian told Pentagon reporters via a video link from Baghdad.

As recently as July, IS was thought to have as many as 10,000 fighters in Mosul. Since then, coalition estimates have continually revised that number downwards as intelligence indicated many top IS officials and their families had fled Mosul for the group's Syrian stronghold of Raqqa.

Iraqi militia leaders also told VOA there was evidence many of the foreign fighters who had once been based in Mosul were leaving.

Additionally, the terror group's attempt to reinforce Mosul has been "limited" due to U.S. and coalition airstrikes.

"Kind of trickling in," Dorrian said. "What you see is small formations, single digit fighters, people with backpacks and things like that."

"They can't move in large columns, formations and convoys," he said.

According to the officials, those IS fighters who do make it to Mosul are often coming from areas to the north, retreating from towns and villages that have fallen to U.S. and coalition-backed ground forces.

Still, U.S. military officials are expecting the IS fighters left in Mosul to put up a tough fight and use a variety of tactics, including oil fires and chemical weapons, to turn Iraq's second largest city into "hell on earth."

"They show no signs of trying to leave," Dorrian said. "They're fixed in place. That's a good situation for us," he added, referring to the coalition's air power adding,