Children escaping Syria's al-Raqa have been "tormented" by years of living under the rule of the "Islamic State of Iraq and Syria" (ISIS), Save the Children said Monday (August 28th).

The non-governmental organisation warned it could take decades for young people from the ISIS stronghold to overcome their psychological injuries, AFP reported.

Save the Children interviewed children and their families who escaped the city, where the Syrian Democratic Forces (SDF) have been battling to defeat ISIS.

"Al-Raqa's children might look normal on the outside but inside many are tormented by what they have seen," said Save the Children’s Syria director Sonia Khush.

Up to 25,000 people, almost half of them children, remain trapped in al-Raqa. The UN has called for a pause in fighting to allow remaining civilians to flee.

Save the Children backs safe routes for children and families, but said that was just the beginning of a longer process to ensure their mental wellbeing too.

"It is crucial that the children who have made it out alive are provided with psychological support to help them deal with the trauma of witnessing senseless violence and brutality," said Khush.

"We risk condemning a generation of children to a lifetime of suffering unless their mental health needs are addressed."