Fighting raged for a third day on January 22 between the Islamic State group and Kurdish forces in Syria after IS attacked a prison housing jihadists, with the violence killing nearly 90 people, a monitor said.
The assault on Ghwayran prison in the northeastern city of Hasakeh is one of IS's most significant since its "caliphate" was declared defeated in Syria nearly three years ago.
"At least 28 members of the Kurdish security forces, five civilians and 56 members of IS have been killed" in the violence, said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
IS launched the attack late on January 20 against the prison, which houses at least 3,500 suspected members of the jihadist group, including some of its leaders, the Observatory said.
The jihadists seized weapons and freed several fellow IS fighters, said the Britain-based monitor, which relies on sources inside war-torn Syria.
Hundreds of jihadist inmates had since been recaptured but dozens were still believed to be on the run, it added.
With air support from the US-led coalition, Kurdish security forces have encircled the prison and are battling to control surrounding neighbourhoods, which jihadists have used as a launchpad for their attacks.
The Kurdish-dominated Syrian Democratic Forces (SDF) said "fierce clashes" broke out in neighbourhoods north of Ghwayran, where it carried out raids and killed more than 20 IS fighters.
An AFP correspondent saw Kurdish fighters raiding homes near the jail in search of militants while coalition helicopters flew overhead.
In one location, Kurdish fighters gathered around five bloodied corpses of suspected IS fighters along a roadside, the correspondent said.
The US condemned the IS attack, praised the SDF's response and noted that IS fighters have been trying to free jihadist prisoners for more than a year.
"It is a credit to the diligent, capable efforts of the SDF and Global Coalition to Defeat ISIS Forces that they were able to thwart numerous attacks during that period and limit the severity of this one," State Department spokesman Ned Price said in a statement, using another acronym for IS.
The battles have triggered a civilian exodus from neighbourhoods around Ghwayran, with families fleeing in the harsh winter cold as Kurdish forces closed in.
"Thousands have left their homes near the prison, fleeing to nearby areas where their relatives live," Sheikhmous Ahmed, an official in the autonomous Kurdish administration, said.
Not all the displaced found safe haven.
"We don't know where we are going," said Abu Anas, who was forced out of his home on January 22.
"We have no one but God," he said as he fled on foot with his wife and four children.
IS has carried out persistent attacks against Kurdish and government targets in Syria since the rump of its once-sprawling proto-state was overrun in March 2019.
Most of them have targeted remote military outposts and oil installations, but the Hasakeh attack could mark a new phase in the group's resurgence.
An IS video released on January 22 by the group's Amaq news agency purported to show armed jihadists infiltrating the prison at the start of the operation.