Clashes between the United States-backed YPG, the PKK terrorist group’s Syrian wing, and Daesh militants continued for a fourth day on Sunday in northeastern Syria, pushing the death toll higher.

The standoff followed a bold assault by Daesh extremists who broke into Gweiran Prison, which houses thousands of its members, enabling an unknown number of militants to escape and hold hostages. At least 27 YPG members were killed.

The U.S-led coalition said the YPG, with its assistance in the form of surveillance, intelligence and airstrikes, had contained the threat.

But several dozen militants remained holed up in one wing of the prison, to the north and in adjacent buildings.

More than 3,000 suspected Daesh militants, including over 600 minors, are held in Gweiran, the largest of a dozen detention facilities in Syria housing militants.

The United Nations children's agency, UNICEF, called for the release of the detained children, warning that violence may spread to other prisons or in camps holding families and children of suspected Daesh members in Syria.

"While it is militarily defeated, Daesh remains an existential threat to the region," said U.S. Maj. Gen. John Brennan, commander of the Combined Joint Task Force-Operation Inherent Resolve. "Due to its severely degraded capability, Daesh’s future survival is dependent on its ability to refill its ranks through poorly-conceived attempts" like the prison attack.

The coalition said the Daesh militants seized arms from prison guards before killing them and attempted to destroy a new, more secure facility under construction next to the Gweiran Prison.

Siamand Ali, a spokesperson for the YPG, said Daesh militants attempted two attacks Sunday on the prison, also known as al-Sinaa prison. One attack was from militants holed up nearby and another from outside the city of Hassakeh, where the prison is located. Both were foiled, Ali said.

Between 150 and 200 militants were believed holed up in the northern wing of the prison and an adjacent residential area, including the Zuhour neighborhood which was cordoned off by security forces, Ali added.

Earlier Sunday, a Hassakeh resident said warplanes from the U.S.-led coalition flew over the prison breaking the sound barrier. The resident, who spoke on condition of anonymity for fear of retribution, said the U.S.-backed YPG forces were heard calling on Daesh militants in the prison and in surrounding buildings to turn themselves in.

The Daesh group claimed responsibility for the attempted prison break on its Aamaq news service.

The total number of fugitives remains unclear.

Freeing convicts and imprisoned comrades has been a main tactic of the group.

During their 2014 surge that overwhelmed territory in Iraq and Syria, Daesh carried out multiple prison breaks.

The attack launched Thursday evening was the biggest by Daesh militants since the fall of the group’s "caliphate" in 2019. Its demise came after Daesh lost its last territory in Syria following a military campaign spanning years backed by the U.S.-led coalition in Iraq and Syria.

It is also known that the YPG frequently uses the prisons and on occasion, frees Daesh members. In late 2021, reports said that former Daesh fighters were being released from prisons controlled by the YPG in the country's northeast in exchange for money under a "reconciliation" scheme.

The Guardian reported that prisoners jailed without trial can pay an $8,000 fine to be freed, citing interviews with two men who had been released and official documents.

Since the reconciliation scheme's implementation in 2019, it is unclear how many people have been able to buy their freedom in this way. The releases pose a significant security risk inside and outside Syria and raise the prospect that individuals who committed grave crimes will not face true justice.

The YPG commits rights violations under the guise of fighting the Daesh terrorist group without anyone holding them accountable. Local people living in areas held by the YPG have long suffered from its atrocities, as the terrorist group has a notorious record of human rights abuses in Syria, ranging from kidnappings, the recruitment of child soldiers, torture, ethnic cleansing and forced displacement.

The U.S. has primarily partnered with the YPG in northern Syria in the fight against the Daesh terrorist group. Turkey strongly opposes the YPG's presence in northern Syria, which has been a major sticking point in strained Ankara-Washington relations. The U.S. has provided military training and thousands of truckloads of weaponry to the YPG, despite its NATO ally's security concerns.

Turkey has aimed to prevent the YPG from establishing a de facto autonomous region in northern Syria, which would border Turkey and connect the so-called northwestern Afrin canton to the Kobani and Jazira cantons in the northeast. Ankara describes this as a "terror corridor" posing a grave security threat to its national security, underlining its possible impact on the PKK’s activity around Turkish borders.

In its more than 40-year terror campaign against Turkey, the PKK – listed as a terrorist organization by Turkey, the U.S. and the European Union – has been responsible for the deaths of 40,000 people, including women, children and infants