The Islamic State group attacked a Kurdish-run jail in northeast Syria on Thursday, freeing fellow jihadists, a war monitor reported without specifying how many escaped.

A car bomb hit the entrance of the Ghwayran prison and a second blast went off in the vicinity before IS jihadists attacked Kurdish security forces manning the facility, the Britain-based Syrian Observatory for Human Rights said.

“A number of prisoners managed to escape,” said the Observatory which relies on a network of sources inside Syria. It did not specify how they managed to break out.

Ghwayran is one of the largest facilities housing IS fighters in northeast Syria, Observatory head Rami Abdul Rahman told AFP.

The Kurdish-led Syrian Democratic Forces confirmed the rare attack in a statement but did not mention any prisoners fleeing.

“A new insurgence and attempted escape by Daesh terrorists detained in Ghwayran prison in al-Hasaka in conjunction with an explosion of a car bomb,” it said, using an Arabic acronym for IS.

It blamed the attack on “Daesh sleeper cells, who infiltrated from the surrounding neighbourhoods and clashed with the internal Security Forces.”

The Observatory said the SDF has dispatched reinforcements to the prison and cordoned off the area.

Aircraft belonging to the US-led international coalition battling IS hovered over the facility and dropped flares in its vicinity, the monitor added.

The coalition was not immediately available for comment.

The Islamic State 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 harass Syrian government and allied forces.