In this Monday, June 16, 2014 file photo, demonstrators chant pro-Islamic State group slogans as they wave the group's flags in front of the provincial government headquarters in Mosul, Iraq. (Uncredited/AP)

The Obama administration announced Wednesday the deployment of up to 450 additional military advisers to Iraq, deepening U.S. involvement in the war against the Islamic State and underscoring the fragility of a U.S. strategy that rests on the abilities of local forces.

The new troops, once in place, will bring the number of American service members in Iraq to around 3,500. The soldiers, who will be stationed at Taqaddum, an air base near the militant-held city of Ramadi, are expected to be focused on assisting Iraqi forces and tribal fighters prepare for an offensive to reclaim the western city, which fell to Islamic State militants in May following a retreat by Iraqi forces.

“This train, advise, and assist mission builds on lessons learned during the past several months,” the White House said in a statement. But recent months have revealed the deep-seated weaknesses of Iraqi troops, who abandoned their posts en masse a year ago in the northern city of Mosul. Since then they have made only halting progress against Islamic State militants, despite help from U.S. and allied airstrikes and Shiite paramilitary fighters who at times who have shouldered the bulk of the fighting.

The new mission at Taqaddum adds to a constellation of other sites where U.S. and allied forces are assisting Iraqi fighters, including five training bases throughout the country. But U.S. military leaders, mindful of President Obama’s prohibition on sending U.S. troops into renewed combat in Iraq, have keep their troops well clear of Iraqi forces skirmishes with the Islamic State.

The Pentagon said the new forces would advise Iraqi troops, including the Iraqi Army’s 8th Division, and would facilitate cooperation between the Iraqi government and Sunni tribal fighters. “This decision does not represent a change in mission, but rather adds another location for [the Defense Department] to conduct similar activities in more areas in Iraq,” the department said in a statement.