dk_photos/iStock/Thinkstock(MOSUL, Iraq) — American military advisers have at times entered the city of Mosul accompanying Iraqi forces fighting to retake the city from ISIS, a U.S. military spokesman said Wednesday.

Since the start of the Iraqi offensive to retake Mosul in mid-October, U.S. officials have not confirmed whether American advisers would operate in the city accompanying Iraqi forces while remaining behind the front lines.

“They have been in the city at different times, yes,” said Colonel John Dorrian, the U.S. military spokesman for Operation Inherent Resolve, in response to a question about whether American military advisers have entered Mosul as part of the Iraqi offensive. Dorrian made his comments during a video briefing from Baghdad with Pentagon reporters.

American military advisers are required to stay behind front lines at military headquarters assisting Iraqi and Kurdish forces involved in the Mosul offensive. However, American special operations forces might come closer to combat situations as they assist Iraqi special operations forces engaged in the fight.

Speaking broadly about the adviser role in the Mosul operation, Dorrian said “they’ve advised the Iraqi Security Forces as they’ve moved forward. They remain behind the forward line of troops.”

Dorrian declined to provide specifics about when or where the American advisers entered the city at various times.

Since the offensive began in mid-October, Iraqi forces have faced tough resistance from ISIS fighters as they pushed into the eastern part of the city. Despite significant casualties, Iraqi forces now control two-thirds of the eastern side of the city that is essentially divided in two by the Tigris River.

Dorrian said the coalition has made adjustments in recent weeks to accelerate “phase two” of the push into Mosul, namely the doubling of advisers involved in the operation to 450.

It was unclear how many of the advisers were American. As of January 4, there are 4,936 American military forces in Iraq and another 3,904 forces from other coalition countries, officials said.

Last week, Iraqi forces started pushing into Mosul from three axes — an operation that Dorrian said “is starting to really make things very difficult for the enemy.”

He added that once Iraqi forces reach “the river, they’re going to go into the west side and then, you know, it will be another very tough fight there as well.”

Copyright © 2017, ABC Radio. All rights reserved.