USA -backed Syrian forces captured 41 positions held by ISIL militants and destroyed their fortifications in the last tiny pocket they hold in eastern Syria amid fierce fighting, a spokesman said Sunday.
"Mustafa Bali, an SDF spokesman, tweeted Saturday, "#SDF started to move on to the last village remaining under jihadists' control.
The SDF had handled the last 10 days "patiently" as more than 20,000 civilians were evacuated from the besieged IS enclave, Bali said.
Bali said heavy fighting was going on inside Baghouz on Sunday, adding that an ISIL counterattack was foiled early in the day.
The SDF, backed by air strikes carried out of the US-led coalition, has driven out IS from towns and villages in north-eastern Syria in recent months.
Four years ago, the militants controlled territory the size of Britain and millions of people, but Major General Christopher Ghika, the deputy commander of the United States coalition fighting the group, on Thursday said that "now less than one percent of the original caliphate" remains.
Trump's surprise announcement in December that he was withdrawing American troops from Syria helped trigger the resignation of his defense secretary, Jim Mattis, and sent USA military officials scrambling to construct a withdrawal plan that preserves as many gains as possible.
Syrian opposition activists say Islamic State militants have attacked US -backed fighters near an oil field in the country's east, triggering airstrikes by the USA -led coalition.
Remaining in an area of fields and farmhouses less than a few square kilometres are up to 600 ISIS fighters and their families, many of them foreigners.
President Donald Trump announced in December he was pulling all 2,000 U.S. troops out of Syria, saying the battle against Islamic State there was nearly won. "They are trying to blend in because there are so many [civilians]".
Referring to future USA troop levels in Iraq, Votel said: "I think it's going to remain more or less steady".
The SDF official also said high-level Islamic State commanders had not been captured yet.
At least 48 suspected ISIS members were among them, according to the Britain-based Syrian Observatory for Human Rights.
Trump said in December that he had ordered a complete troop withdrawal from Syria, a shock announcement that left the Kurds scrambling for new allies.
It is also unclear whether the United States will be able to satisfy the security concerns in Syria of its North Atlantic Treaty Organisation ally Turkey without sacrificing the interests of USA -backed Kurdish fighters there.
While the Kurdish People's Protection Units (YPG) have been a key U.S. ally in the fight against ISIL, Turkey views them as "terrorists".
As the SDF closed in, there were reports that two Canadian women and their children who had been living in the ISIS-controlled area had surrendered to the US -backed forces, CNN and CBC reported Sunday.