U.S.-Backed Forces Retake Syrian Prison From Islamic State

An SDF spokesman said Wednesday that al-Sina’a prison was under its entire control, with all Islamic State members having surrendered.

For Islamic State, the attack on the prison was a reassertion of the group’s ability to carry out large-scale violence and threaten a high-value facility held by U.S.-backed forces. The complex attack, involving sleeper cells and an uprising among prisoners inside the facility, was more ambitious than any attempted in Syria since 2019.

The prison break illustrated the challenges of eradicating Islamic State, an organization that has shown an ability to repeatedly transform itself to adapt to shifting political currents and security conditions in Iraq and Syria.

The group has its origins in the homegrown insurgency against the U.S. invasion of Iraq in 2003 and later became a transnational extremist group and eventually a self-proclaimed state ruling over millions of people in Iraq and Syria.

Although it was ultimately crushed, the prison break could be a significant propaganda victory in Islamic State’s efforts to continue to inspire its world-wide following, analysts said.

“The symbolic impact of this in the grand scheme of what ISIS is trying to do means that this is going to go down as a pivotal moment in its history in Syria and globally as well,” said Charlie Winter, director of research at ExTrac, a conflict-analysis firm.

The attack began nearly a week ago with suicide bombings and a revolt among Islamic State members inside the prison. That sparked days of fighting that spilled into the neighborhoods surrounding the facility.

As the operation to retake the facility culminated on Wednesday, the SDF said it carried out a building-by-building sweep of the prison grounds in an attempt to regain full control of the facility.

The SDF said earlier on Wednesday that 1,000 Islamic State fighters had surrendered during the fighting. Islamic State claimed to have freed 800 people from the prison but the SDF denied that assertion. Some 200 people were involved in the initial attack on the prison, which involved a revolt inside the facility, the SDF has also said.

The intense fighting resulted in the biggest U.S. combat deployment in Syria in years. U.S. officials said 100 to 200 U.S. troops were part of a response that also included airstrikes, surveillance and Bradley Fighting Vehicles, the heaviest vehicle at the disposal of the U.S. forces in Syria.

American soldiers used the Bradleys to create specific pathways within Hasakah, and fired on those pathways, defense officials said. The deployed troops are a significant part of the roughly 900 U.S. soldiers who are stationed in Syria supporting Kurdish-led Syrian militias in their fight to eradicate Islamic State.

The U.S. didn’t participate in negotiations with Islamic State members inside the prison, but had advisers with the SDF forces leading those talks, U.S. officials said.

The commander of U.S. forces in Iraq and Syria called for an investigation into the circumstances of the attack, and expressed concern about other prisons in northeastern Syria holding thousands of Islamic State prisoners.

“The makeshift prisons throughout Syria are a breeding ground for Daesh’s failed ideology,” said Maj. Gen. John W. Brennan in a statement on Wednesday.

The SDF said just after midnight Wednesday that over the last two days it had freed 23 people who had been taken hostage by Islamic State, including prison staff and others.

As the battle wore on, concern has grown about the fate of the 850 children as young as 12 held in the prison and trapped with Islamic State fighters who were still in control of a section of the facility. Many of the children are boys who were detained in 2019 after the fall of Islamic State’s last territorial enclave in Syria, according to the charity Save the Children.

The SDF accused Islamic State on Wednesday of using the boys and teenagers as human shields. It wasn’t immediately clear what happened to the children.

The U.N. children’s agency Unicef said late Tuesday that it was concerned about reports that children trapped in the prison may have been forced to participate in the fighting between prisoners and security forces, and about reports that some had been killed.

“These children should never have been held in military detention in the first place. The violence they are subjected to may amount to war crimes,” said Unicef Executive Director Henrietta Fore.

Some 45,000 people have been forced to flee their homes in the neighborhoods around the prison, according to the U.N. Office for the Coordination of Humanitarian Affairs.

The attack came after a lull in Islamic State violence in Syria. In the desert expanse in the center of the country, which has been the focus of the group’s insurgency in recent years, the group carried out only 11 attacks and killed fewer government soldiers than it had at any time since 2019, according to Gregory Waters, an analyst with the Counter Extremism Project who tracks Islamic State activity in the area.

Immediately following the prison break, Islamic State launched a series of other attacks within areas held by the SDF in northeastern Syria, suggesting a coordinated campaign, analysts said. The Jan. 20 prison break coincided with another attack in which Islamic State gunmen killed 11 Iraqi soldiers as they slept in their camp.

“ISIS has shifted its operational focus from quantity to quality,” said Mr. Winter, the conflict analyst.

Write to Jared Malsin at jared.malsin@wsj.com and Nancy A. Youssef at nancy.youssef@wsj.com