US-backed fighters have captured ISIS's encampment in Baghouz as some of the cornered militants refuse to surrender.
The Syrian Democratic Forces have been attacking the ISIS camp in the village of Baghouz since January.
SDF spokesman Mustafa Bali said on Tuesday that the SDF "is in control of the Daesh encampment area in Baghouz".
"This is not a victory announcement but significant progress in the fight against Daesh," Mr Bali said.
The military operation is continuing because "a group of ISIS terrorists who are confined in a tiny area still fight back", he said.
#SDF is in control of Daesh encampment area in #Baghouz. This is not a victory announcement, but a significant progress in the fight against Daesh. Clashes are continuing as a group of ISIS terrorists who are confined into a tiny area still fight back.
— Mustafa Bali (@mustefabali) March 19, 2019
SDF commander Zana Amedi said that the encampment was "completely under SDF control".
He shared an image of the territory left in ISIS hands earlier in the day, showing the cleared camp and a sliver of territory on the Euphrates river bank.
Earlier, the SDF said it captured 157 militants trying to escape Baghouz.
Its special forces had anticipated a breakout attempt by desperate fighters.
“In a well-ordered operation our units monitored a group of terrorists, trailing and capturing 157 with their full military equipment,” the SDF said.
“The arrested terrorists are foreign nationals with long fighting experience."
Mr Bali declined to specify the nationalities of the captured fighters and did not say when the operation took place.
Meanwhile, hundreds of sick and injured ISIS militants who were captured when the SDF took over the encampment were taken to military hospitals on Tuesday and had been treated humanely, he said.
In the past two months about 5,000 fighters have surrendered, among more than 60,000 people who have left Baghouz, a tiny farming village in the Euphrates River valley in eastern Syria.
After more than two months of fitful assaults and pauses for civilians to escape and militants to surrender, the SDF estimates there may yet be 5,000 more people in Baghouz.
The militant encampment is flat farmland, now crammed with abandoned vehicles and crowded with makeshift shelters.
It is the only territory left in Iraq and Syria controlled by ISIS, which in 2014 declared a caliphate and once ruled more than a third of both countries.
While the group’s eventual defeat in Baghouz is inevitable, ISIS's leadership and its supporters have already vowed to regroup.
On Monday night, ISIS released an audio recording from its spokesman, known only as Abu Hassan Al Muhajir, saying the group would remain strong.
"Do you think the displacement of the weak and poor out of Baghouz will weaken [ISIS]?” he asked. “No."
Meanwhile, the force announced on Tuesday that an Italian national fighting alongside it had been killed.
Lorenzo Orsetti, 33, was killed in battle on Sunday as he fought ISIS in the village of Baghouz, Mr Bali said.
"Two days ago... he was at the forefront of the fighting and he died in battle," he told AFP.
"He was a frontline fighter in the ranks of the People's Protection Units," a Kurdish force leading the SDF, Mr Bali said.
"He participated in more than one battle and more than one SDF campaign."
Orsetti fought to defend the Kurdish enclave of Afrin in north-west Syria before it was overrun by Turkish-backed Syrian rebels a year ago, Mr Bali said.
ISIS published a photograph of the dead fighter and a snapshot of his healthcare card on its social media channels Monday, claiming to have killed him in Baghouz.
Orsetti's father told Italian newspaper Corriere della Sera he and his wife were "very proud" of their son.
A former waiter and chef from Florence, Orsetti travelled to Syria in September 2017 as an observer but felt "increasingly involved", his father said.
