International rights groups, including Save the Children and Human Rights Watch have previously said that 700 boys had been in the Ghwayran jail before the January 20 operation.

Aged between 12 and 18, they include many who had adult relatives inside the prison and were transferred from nearby displacement camps housing thousands of children of jihadist fighters.

"UNICEF met with some of the children still detained in the Ghwayran detention centre," the UN's child agency said in a statement.

"Despite some of the basic services now in place, the situation of these children is incredibly precarious," it added, without specifying how many minors were still detained.

Farhad Shami of the Kurdish-led Syrian Democratic Forces told AFP that "hundreds" of minors were still being held in Ghwayran, refusing to disclose an exact figure.

"They are being kept in a safe place," he said

The IS prison break attempt from the Ghwayran jail in Hasakeh city triggered a week of clashes inside and around the Kurdish-run facility, leaving hundreds dead, before Kurdish-led forces recaptured the jail.

It was the largest jihadist operation in Syria since the group's territorial defeat in 2019.

UNICEF said it was working to immediately provide care for the minors and confirmed that it "is ready to help support a new safe place in the northeast of Syria to take care of the most vulnerable children".

On Sunday, the SDF said in a statement that UNICEF was the first UN agency granted permission to visit the jail since the attack.

"The delegation was provided with information on the status of the Deash-linked teenagers," the SDF added, using an Arabic acronym for IS.

Video footage of the visit posted on social media networks showed around a dozen boys, many covered in blankets, in a prison cell.

Kurdish authorities have repeatedly blamed the international community for failing to support efforts to rehabilitate and repatriate jihadist children.

Ghwayran housed at least 3,500 IS suspects before last month's attack.