WASHINGTON — The U.S.-led military coalition in Iraq has doubled the size of its adviser corps, reflecting the intensified effort to help Iraqi forces retake the Islamic State stronghold of Mosul, a U.S. officer said Wednesday.

U.S. Air Force Col. John Dorrian, speaking from coalition headquarters in Baghdad, told reporters at the Pentagon that the adviser corps has expanded to roughly 450 “in the last couple of weeks,” since Iraqi forces launched what they call “phase two” of the Mosul campaign.

The advisers perform a range of roles, from accompanying Iraqi troops as they move around the battlefield to providing engineering and intelligence support. They are not meant to be involved in direct combat, although they have come under fire at times. One adviser, Navy Chief Petty Officer Jason C. Finan, was killed by a roadside bomb on Oct. 20 near Mosul.

Dorrian said the advisers are not on the front line of combat.

“They remain behind the forward line of troops,” Dorrian said, but added that they have entered the city itself “at different times.”

The total number of U.S. troops in Iraq is 4,935, by the Pentagon’s count. They include trainers, security forces and other support troops.