President Donald Trump has said he expects all territory held by so-called Islamic State will be reclaimed next week.
"It should be announced, probably sometime next week, that we will have 100% of the caliphate," the president told foreign ministers from the Global Coalition to Defeat ISIS.
Mr Trump caveated, however, that he wanted to "wait for the official word".
US officials have briefed that IS has been driven out of 99.5% of its territory and retains control of only two square miles in the Middle Euphrates River Valley.
In December the White House announced America’s 2,000 troops would be pulled out of Syria in 30 days – leading to the resignation of the US Defense Secretary Jim Mattis.
Mr Trump later tweeted that troops would be brought home “slowly".
President Trump described Syria as an 'ISIS loaded mess' in December
The withdrawal is a "tactical change... not a change in the mission", US Secretary of State, Mike Pompeo, said.
He added that an "era of decentralised jihad" was beginning.
Military officials have raised concerns that the US pull-out will imperil gains against IS and that the organisation could eventually regroup.
A United Nations report said that IS fighters "continue to pose the main and best-resourced international terrorist threat".
It added that while IS militants are under "intense military pressure" in their remaining territory, they have "shown a determination to resist and the capability to counter-attack".