U.S.-backed fighters said they had taken positions in Islamic State's last enclave in eastern Syria and air strikes pounded the tiny patch of land beside the Euphrates River early on Monday, a Reuters journalist said.
Smoke rose over the tiny enclave as warplanes and artillery bombarded it. Another witness said the jihadists had earlier mounted a counter attack.
"Several positions captured and an ammunition storage has been blown up," said Mustafa Bali, a spokesman for the Syrian Democratic Forces (SDF) militia, on Twitter late on Sunday.
The enclave resembles an encampment, filled with stationary vehicles and rough shelters with blankets or tarpaulins that could be seen flapping in the wind during a lull in fighting as people walked among them.
Backed by air power and special forces from a U.S.-led coalition, the SDF has pushed Islamic State from almost the entire northeastern corner of Syria, defeating it in Raqqa in 2017 and driving it to its last enclave at Baghouz last year.
But while its defeat at Baghouz will end its control of populated land in the third of Syria and Iraq that it captured in 2014, the group will remain a threat, regional and Western officials say.
The SDF has waged a staggered assault on the enclave, pausing for long periods over recent weeks to allow surrendering fighters, their families and other civilians to pour out.
Since Jan. 9, more than 60,000 people have left the enclave, about half of them surrendering Islamic State supporters including some 5,000 fighters, the SDF said on Sunday.
People leaving the area have spoken of harsh conditions inside, under coalition bombardment and with supplies of food so scarce some resorted to eating grass.
Last month, the SDF said it had found a mass grave in an area it captured.
Still, many of those who left Baghouz have vowed their allegiance to the jihadist group, which last week put out a propaganda film from inside the enclave calling on its supporters to keep faith.
Suicide attacks on Friday targeted families of Islamic State fighters attempting to leave the enclave and surrender, killing six people, the SDF said.
Late on Sunday, the Kurdish Ronahi TV station aired footage showing a renewed assault on the enclave, with fires seen to be raging inside and tracer fire and rockets zooming into the tiny area.
The SDF and the coalition say the Islamic State fighters inside Baghouz are among the group's most hardened foreign fighters, though Western countries believe its leader, Abu Bakr al-Baghdadi, has left the area.