US-backed Syrian forces have made slow advances into the edge of the last village held by the Islamic State group, battling militants holed up in underground tunnels.
The battle opened on Sunday evening with large explosions and smoke rising into the air over Baghouz, on the Euphrates River in eastern Syria, as the Syrian Democratic Forces (SDF) battered the village with artillery and gunfire, hitting an IS ammunition dump.
On Monday, the thuds of renewed artillery and heavy weapons fire could be heard. An air strike also hit the IS-held pocket.
Some 500 IS fighters are believed to be still in the territory, along with possibly 3,000 to 4,000 civilians, including women and children. They are mainly family members who remained after thousands of civilians streamed out of Baghouz over the past week during pauses in the fighting.
Mustafa Bali, of the Kurdish-led SDF, said the forces were moving cautiously on the ground, adding that the militants were dug in and hiding in tunnels.
The area is also believed to be laced with landmines and booby traps.
"If, as we advance, we notice there are civilians, we will do all we can to evacuate them from the battlefield," Mr Bali said.
The Britain-based Syrian Observatory for Human Rights, a war monitor, said SDF fighters had captured seven IS gunmen in Baghouz since Sunday.
A senior US defence official said that it would not be a surprise, based on current conditions, if it took another couple of weeks to finish "mopping up" the IS enclave.
The capture of Baghouz would be a milestone in the four-year campaign to defeat the group's so-called "caliphate" that once covered a vast territory straddling both Syria and Iraq.
