Clashes broke out Saturday between Kurdish forces and ISIS fighters near a Syrian prison where dozens of extremists are still holed up, a war monitor said.

An ISIS assault on the sprawling Ghwayran prison complex near the northeastern Syrian city of Hasakeh on January 20 sparked days of heavy fighting that has left some 260 people dead, and a bulldozer on Saturday shoveled corpses onto a truck to take some for burial.

The US-backed Syrian Democratic Forces (SDF) announced they had recaptured the prison on Wednesday, but that mop-up operations continued.

On Saturday, there were “clashes in the vicinity of the prison between the Syrian Democratic Forces and Kurdish security forces on the one hand, and members of ISIS who are hiding in the area,” the Syrian Observatory for Human Rights said.

The war monitor, which relies on a network of sources inside Syria, said that four ISIS fighters took a local official and three civilians hostage for hours, holding them in a residential building near the prison.

Kurdish forces later freed the hostages and killed three ISIS fighters.

An AFP correspondent earlier reported that US troops and Kurdish-led forces surrounded the building and deployed snipers on nearby rooftops, reporting there was intermittent shooting.

The SDF said Wednesday some 3,500 ISIS members had surrendered, but that holdout ISIS fighters had barricaded themselves inside the prison facility.

ISIS in prison basement

The ISIS gunmen are in “cellars that are difficult to target with air strikes or infiltrate” the Observatory said.

SDF officials estimate that between 60 and 90 ISIS fighters were still in the basement and the ground floor above it.

Kurdish forces have repeatedly called for ISIS gunmen to surrender.

“Our forces have not used force with them so far,” Farhad Shami, who heads the SDF’s media office, said Saturday.

On Saturday, an AFP correspondent saw a truck carrying piles of bodies away from the area near the prison, corpses believed likely to be those of ISIS fighters.

A bulldozer dumped more bodies inside the truck, which then headed to an unknown location.

Shami said that the bodies would be buried in “remote, dedicated areas” under SDF control.

The Kurdish component of the SDF, known as the People’s Protection Units (YPG), published a video showing a handful of ISIS members who surrendered on Friday. An SDF source estimated their number at around 10.

In the video, two men carried away someone on a stretcher.

Kurdish-led forces have banned journalists from freely accessing the Ghwayran neighborhood or approaching the prison since the start of the attack.

The fighting has killed more than 260 people, including around 180 extremists, 73 Kurdish-led fighters and seven civilians, the Observatory said, adding that the death toll is likely to increase.

The violence forced 45,000 people to flee Hasakeh, the United Nations said. Many took refuge in their relatives’ homes, while hundreds others have been sleeping in the city’s mosques and wedding halls.