Syrian Kurdish forces end mop-up operations in IS-hit jail

US-backed Kurdish forces on Sunday said they had defeated all Islamic State group fighters left inside the Syrian jail that the jihadists stormed 10 days ago sparking battles that left over 330 dead.

The Kurdish-led Syrian Democratic Forces (SDF) announced the end of its mopping-up campaign inside the prison "after ending the last pockets in which IS terrorists were present", it said in a statement.

IS fighters on January 20 launched their biggest assault in years on the Ghwayran prison in the Kurdish-controlled northeastern Syrian city of Hasakeh, aiming to free fellow jihadists.

After six days of intense fighting, the SDF announced on Wednesday they had recaptured the prison, but intermittent clashes continued until Saturday between Kurdish fighters and jihadists near the jail.

Several IS fighters had been holed up in "northern dormitories" inside the prison, but the SDF on Sunday said they been defeated.

IS gunmen had been hiding in prison "cellars that are difficult to target with air strikes or infiltrate," the Syrian Observatory for Human Rights said.

Hunt for fugitives

The war monitor, which relies on a network of sources inside Syria, said operations were still ongoing near the prison hunting for escaped IS fugitives.

"Dozens of IS members managed to escape from Ghwayran prison... in the early hours of the attack," the war monitor said.

It reported that 20 IS fighters had surrendered on Saturday, while the SDF killed another five in an exchange of fire inside the prison.

The Britain-based group said that 332 people had been killed since the onset of the attack, including 246 jihadists, 79 Kurdish-led fighters and seven civilian.

The death toll rose overnight on Sunday after the SDF found over 50 more bodies in prison buildings and nearby areas, the war monitor said.

"The newly discovered bodies were inside and outside the prison," Rami Abdel Rahman, who heads the Observatory, told AFP. 

He said the death toll was likely to rise further, because "there are dozens of people who are wounded, others who are still missing, and information about more casualties" on both sides.

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

A bulldozer dumped more corpses onto the truck, which then headed to an unknown location.

Farhad Shami, who heads the SDF's media office, told AFP that the bodies would be buried in "remote, dedicated areas" under SDF control.

The violence prompted 45,000 people to flee Hasakeh, the United Nations said. Many took refuge in relatives' homes, while hundreds more slept in the city's mosques and wedding halls.

The war in Syria, which broke out in 2011, has killed close to half a million people and spurred the largest conflict-induced displacement since World War II.