Shafaq News / Kurdish-led forces in northeast Syria on Friday found the bodies of 18 fellow fighters inside a prison that the Islamic State group attacked last week, a war monitor reported.

The US-backed Syrian Democratic Forces said Wednesday that they had recaptured the sprawling complex in the city of Hasakeh following a January 20 IS jailbreak attempt that sparked days of clashes inside the facility and in surrounding areas.

But mop-up operations are still underway in the Ghwayran prison where Kurdish forces say dozens of jihadists remain holed up.

During a sweep on Friday, the SDF backed by Kurdish internal security forces "found the corpses of 18 fellow fighters killed by jihadists", the Britain-based Syrian Observatory for Human Rights said.

The war monitor, which relies on a network of sources inside Syria, also reported that an overnight air strike near the jail, carried out by the US-led coalition battling IS, killed seven jihadists.

The death toll since January 20 now stands at over 260, including around 180 IS jihadists, 73 members of Kurdish-led forces and seven civilians, according to the Observatory.

The extremists that remain inside the facility have barricaded themselves in "cellars that are difficult to target with air strikes or infiltrate on the ground", the Observatory said.

Kurdish forces "are looking to starve jihadists into surrendering", said Observatory head Rami Abdul Rahman, adding that those holding out were diehard IS followers.

An SDF official said around 60 IS fighters were holed up in a basement and a ground floor above it.

"We believe there are no minors among them," he told AFP on the condition of anonymity as he was not authorised to comment on the issue.

The jihadists have been given a deadline to surrender and if no progress is made they will be dealt with "firmly", he said, without specifying a time frame.

The Ghwayran jail assault was the most high-profile IS attack since the jihadists lost their "caliphate" nearly three years ago.

According to the SDF, around 3,500 inmates and IS attackers have surrendered to its forces since the start of operations to recapture the prison.

Source: AFP