BEIRUT — The extremist Islamic State group staged a brazen assault on a prison in northeastern Syria, provoking intense clashes with the U.S.-backed Kurdish-led forces and causing dozens of casualties on Friday.

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       The attack on Ghwaryan prison in the Kurdish-controlled area of Hasakah province started Thursday night with a revolt by inmates and the detonation of a car bomb near the jail by Islamic State fighters. Fighting then spread into the town.

       “Our forces killed around 20 terrorists that tried to attack the prison,” said Mervan Qamishlo, a spokesman for the Syrian Democratic Forces. “Now there are clashes taking place in the neighborhoods near the prison, and Daesh is hiding behind civilians and using them as human shields.” Daesh is the Arabic acronym for the Islamic State.

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       He said at least three civilians were killed in the clashes and confirmed a statement by the area’s internal security forces that one of its members had been killed and seven wounded. Seven inmates were also killed, the SDF reported.

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       Almost three years after the Islamic State lost its final strip of territory in Syria, some 5,000 alleged members of the group remain in pretrial detention across the country’s northeast, which is ruled by a U.S.-backed Kurdish administration. Cells are overcrowded, access to health care is limited, and there are hundreds of children among the imprisoned.

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       The region’s leaders routinely appeal for help from the international community, pointing out that many of the detainees are foreign, and that they cannot bear the burden alone.

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       Although the British government helped expand the prison in Hasakah last year, Syrian and coalition officials have repeatedly warned that it remains poorly defended and vulnerable to attack.

       On Thursday night, inmates aided the prison break by burning plastic materials and blankets in an effort to cause chaos, the SDF said in a statement. It added that 89 prisoners had been recaptured after their escape.

       The U.S.-led coalition issued a statement of its own confirming the clashes and said it provided air support to the ground operations, without providing further details.

       Syria’s state news agency reported electricity blackouts in the center of Hasakah and surrounding neighborhoods, quoting the head of the electricity company in the city who said the clashes had damaged power lines in the area.

       The Islamic State was defeated in 2019 by local forces from Syria and Iraq, backed by a global U.S.-led coalition. At the height of its power, it controlled an area the size of Britain and commanded as many as 100,000 men.

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       Since its defeat, sleeper cells in Syria’s northeast and east provinces have conducted attacks on armed groups, including the Syrian army and the SDF.

       They also remain active in Iraq, where the army said Friday that at least 11 soldiers were killed by militants in the central Diyala province overnight. In photographs provided by a member of their company, the base where an apparent Islamic State ambush had taken place appeared deserted. There were blood stains on the ground.

       Iraqi Prime Minister Mustafa al-Kadhimi used his Twitter account to describe the attack as “terrorist” crime that would not pass without “decisive punishment.”

       Although the Islamic State was officially defeated more than four years ago in Iraq, security forces have struggled to prevent the remaining militants from exploiting security gaps across their territory and the country’s government has yet to address many of the social, economic and political grievances which led to the group’s rise in the first place.

       Loveluck reported from Irbil, Iraq. Ellen Francis in London contributed to this report.

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