Brett McGurk, the US co-ordinator for the Middle East and North Africa, concluded a two-day-visit to Iraq on Monday in which he praised the "tremendous progress" made by Iraqi Security Forces and the Peshmerga in fighting ISIS.
Baghdad and the Pentagon last week announced the long-planned end of the US combat role in Iraq. About 2,500 US troops will remain in Iraq in a training and advisory capacity.
Mr McGurk “confirmed President [Joe] Biden’s commitment to the results of the strategic dialogue with the government of Iraq, underscoring that there are no longer US forces serving in a combat role in Iraq", the White House said.
"This transition was made possible because of the tremendous progress achieved by Iraqi Security Forces, including the Peshmerga, in leading the fight against ISIS."
When ISIS rampaged across vast areas of Iraq in 2014, the ISF crumbled, abandoning bases and military equipment. Later that year, a US-led coalition intervened to push back the extremists' advance.
Mr McGurk met several leaders in Baghdad and Kurdistan, including Iraqi President Barham Salih, Prime Minister Mustafa Al Kadhimi, National Security Adviser Qassim al Araji, and former speaker Mohammed Al Halbousi.
In Erbil, Mr McGurk was accompanied by US ambassador to Iraq Matthew Tueller and met President of the Iraqi Kurdistan Region Nechirvan Barzani and other Kurdish officials.
Mr McGurk said US coalition forces remaining in Iraq would be present at the invitation of the Iraqi government.
The Pentagon confirmed last week that the change in US role still grants its military the right of self-defence.
“We have to assume that threats to US forces remain credible in Iraq," Pentagon spokesman John Kirby said.
"We always have the right and the authority and the capability to defend our troops, to defend our resources. Wherever we are, that doesn’t change."
Mr KIrby said the transition has been long in the making.
US troops "have been working themselves out of offensive combat operations against ISIS for quite some time", he said.
"A vast majority of what they’ve been doing for a while now has been advise, assistant and train.
In effect, about 2,500 US and 1,000 other coalition troops stationed in Iraq will remain there, as they have been acting as advisers and trainers since mid-2020.
ISIS established a self-proclaimed caliphate across large sections of Syria and Iraq from 2014.
It was defeated in Iraq in 2017 after offensives by Iraqi forces, with the support of the coalition that has included more than 80 countries, including Britain, France and several Arab nations.
Even though Iraq declared victory against ISIS in December 2017, the group's remnants still carry out attacks against security forces and civilians and in recent weeks killed several Kurdish fighters in northern Iraq.