Kurdish forces in northeastern Syria on Friday hunted down Islamic State group fighters after an IS attack on a Kurdish-run prison housing fellow jihadists, a war monitor and Kurdish forces said.
The rare attack on Ghwayran prison in Hassakeh province on Thursday saw the jihadists detonate a car bomb near the jail and attack Kurdish forces guarding the facility in an attempt to free some of the group's members, the Kurdish-led Syrian Democratic Forces said.
The Syrian Observatory for Human Rights monitor said "five IS prisoners managed to break out", but it remains unclear whether they have since been killed or recaptured.
The US-led coalition battling IS said "SDF casualties ensued during the attack", but it did not disclose how many.
The assault triggered clashes between the jihadists and US-backed SDF forces around the prison that continued into Friday amid heightened security measures, the Observatory said.
"Clashes are ongoing between IS fighters and (Kurdish) military forces in the area," Observatory director Rami Abdel Rahman told AFP, describing it as one of the largest such attacks by IS since its proto-state was declared defeated in 2019.
"At least six IS fighters have been killed in the clashes," Abdel Rahman said, without specifying casualties among Kurdish security forces.
The SDF, which oversees the jail, said on Friday that it "arrested two IS fighters that tried to escape from the Ghwayran prison" as part of combing operations following the attack.
The jihadists were captured in the vicinity of the jail, it said.
It said IS fighters that carried out the attack were hiding in civilian homes in the neighbourhood of Al-Zuhoor near the jail.
"Exceptional security measures in the vicinity of the prison and surrounding neighbourhoods are ongoing," it said in a statement on Friday morning.
IS fighters "are using civilians in the Al-Zuhoor neighbourhood and areas north of the prison as human shields," it said, adding that IS had killed some civilians in the area.
"Our forces and the relevant security services are moving with great precision and sensitivity to contain these incident."
Ghwayran is one of the largest facilities housing IS fighters in a semi-autonomous region controlled by Kurdish authorities in northeast Syria.
According to Kurdish authorities, more than 50 nationalities are represented in a number of Kurdish-run prisons where more than 12,000 IS suspects are now held.
From France to Tunisia, many of the IS prisoners' countries of origins have been reluctant to repatriate them, fearing a public backlash at home.
IS "remains an existential threat in Syria and cannot be allowed to regenerate," the coalition said in a statement after Thursday's attack.
"Coalition forces will continue to defend against and deter hostile activities against ourselves and our partners."
The IS group's self-declared caliphate, established from 2014, once stretched across vast parts of Syria and Iraq and administered millions of inhabitants.
A long and deadly military fightback led by Syrian and Iraqi forces with backing from the United States and other powers eventually defeated the jihadist proto-state in March 2019.
The remnants of IS mostly went back to their desert hideouts from which they continue to attack Syrian government and allied forces.
Earlier this month, IS fighters shot dead an aid worker with the Kurdish Red Crescent at the Al-Hol camp for displaced people.
Last week, an IS attack near Syria's border with Iraq killed five Syrian pro-regime fighters and wounded 14 others, according to the Observatory.