ISIS is preparing for a protracted fight in Mosul, with many of its foreign fighters remaining in the Iraqi city, U.S. officials told Fox News on Tuesday.
Officials believe that it will take weeks for Iraqi forces to enter Mosul, with concern that the foreign fighters in the city are more ideologically zealous then fighters elsewhere in Iraq.
The cities of Mosul in Iraq and Raqqa in Syria are important to ISIS, and there is a higher portion of capable fighters there, U.S. officials told Fox News.
So far in the first 48 hours of the military operation, Iraqi forces have seen less resistance outside the city. Some ISIS fighters have left Mosul to the west, where the terror group controls territory, including the road and 50 miles west to Tal Afar, officials said.
The western side of Mosul remains open because ISIS controls that territory west of the city, and Iraqi forces and Kurdish peshmerga don’t have access to that area, partly because of geography, but mainly because ISIS controls that area, according to officials.
In previous battles against ISIS in Fallujah and Ramadi, Iraqi security forces were able to approach the city and surround it from safe ground. That is not the case however in Mosul, according to US officials, as Iraqi and Kurdish forces cannot surround the city at the moment.
So far in the battle for Mosul, small groups have left the city but no large groups of ISIS fighters have fled.
There also have not been any large groups of civilians seen leaving Mosul, according to U.S. officials. So far, 7 million leaflets have been dropped by U.S. Air Force B-52 members telling residents in Mosul to stay in their homes, officials said.
At some point, the U.S. military expects senior ISIS leaders to try and leave Mosul and head to Raqqa.
As the battle for Mosul enters the later stages, U.S. officials told Fox News they expect ISIS to use chemical weapons, but the terror group so far has only shown rudimentary knowledge of using them.
ISIS is also burning tires in an effort to mask their movements, but officials told Fox News that it is having no effect on U.S.-led coalition aircraft overhead conducting airstrikes.
While the Pentagon has said publically that more than 100 U.S. special operations forces are embedded with Iraqi counter terrorism service (CTS) and Kurdish peshmerga fighters, Fox News is told that number is much higher -- upwards of 300. The forces are made up of 12-man teams farmed out to various units.
Officials however insist the U.S troops are not on the front lines, and so far, there have been no U.S. troops under attack while embedded with Iraqi forces.
On Monday, Pentagon press secretary Peter Cook reiterated that the Mosul operation was an Iraq-led fight and the U.S. military would be acting in a support role. One group Cook said the US military would not support is Iranian-backed Shia militias.
Cook said so far U.S. Army Apache attack helicopters have not been used in Mosul.
“This is their fight,” said Cook of the Iraqi forces.
“The Iraqis are at the front and Americans are providing in their advisory role, but they are behind the forward line of troops. And they are providing that same sort of advice and assistance that they have in Iraq previously and will continue to do so as this fight progresses,” he added.
Cook said Monday that U.S. forces are located on the outskirts of Mosul and in “harm’s way,” but would remain behind the front lines with the Iraqis in the lead.
“I think it's fair to say that there are Americans at the outskirts of the city, but I'm not going to get into the disposition of every single American,” Cook told reporters. He later said a “small number” of Americans were advising the Iraqi forces on the ground.
Lucas Tomlinson is the Pentagon and State Department producer for Fox News Channel. You can follow him on Twitter: @LucasFoxNews