Story highlights Coalition forces have encountered "stiffening resistance" in recent days

The US military estimates there are about 2,000 ISIS fighters remaining in Raqqa

(CNN) US military advisers helping Kurdish and Arab fighters combat ISIS in Raqqa, Syria are "more exposed to enemy contact" than they were during the battle for Mosul, the spokesman for the US-led coalition said Wednesday.

"They are much more exposed to enemy contact than those in Iraq," US Army Col. Ryan Dillon told reporters at the Pentagon, referring to US and coalition troops that are accompanying local allies in the fight for Raqqa, ISIS' de-facto capital.

Coalition artillery and aircraft have been supporting the Syrian Democratic Forces as they have fought to capture the Syrian city, a battle coalition officials have said will be hard-fought.

Dillon said the US and coalition troops that have entered Raqqa alongside their local allies "are assisting by calling in strikes against enemy forces within the city."

He explained the primary reason for the increased exposure was that US troops are "putting themselves where they need to be" and advising their local allies in smaller formations, closer to front line combat.

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