The military ended its combat mission in Iraq on Thursday, transitioning to a training advisory role.
Under the terms of a July agreement, the United States has been winding down the mission for months against the Islamic State, with about 2,500 service members still in Iraq.
Those troops will remain for now to advise and assist Iraqi security forces, a change that was finalized after technical talks between Washington and Baghdad wrapped on Thursday.
U.S. forces have been in Iraq since 2014 to lead a coalition to defeat the Islamic State after the extremist group took over large swaths of Iraq and Syria. At the height of their power, the group controlled over 110,000 square kilometers of territory with a height of 40,000 fighters.
The military defeat of the group was declared in 2017, but scattered fighters have continued a low-level insurgency.
After the group's defeat, the Biden administration agreed to pull all combat forces by Dec. 31, with a new mission to advise and assist Iraqi forces as they continue to fight ISIS.
A need for constant vigilance: In a statement, Maj. Gen. John Brennan said the U.S. will remain in Iraq to "assist, and enable the ISF, at the invitation of the Republic of Iraq."
"In this new phase, our transformative partnership with Iraq symbolizes the need for constant vigilance. ISIS is down, but not out," Brennan said.
Pentagon press secretary John Kirby told reporters that "we have to assume" that threats to US forces "remain credible in Iraq."