An Australian teenager is believed to have died in a Syrian jail after being held for three years, his family said on Monday as they pleaded for the return of other detained women and children.
Yusuf Zahab, 17, died from "uncertain causes" in northeast Syria at the Al-Sinaa prison, Human Rights Watch said.
Kurdish-led forces have held IS suspects at the prison, which was the site of intense fighting between IS fighters and US-backed troops earlier this year.
"We are heartbroken and angry'', Zahab's family said in a statement released by HRW.
"Yusuf didn't need to die. The previous Australian Government knew about Yusuf's predicament for more than three years'', they added.
Born in Sydney, Zahab was 11 when he was taken to Syria by relatives before being detained by Syrian Democratic Forces in 2019.
He had previously begged for help in audio messages released by the human rights group, and described watching fellow child prisoners being killed in front of him during a raid on the prison.
"There's a lot of bodies, dead bodies and there's a lot of injured people screaming from pain'', he had said.
Australia's Department of Foreign Affairs said it was still seeking to confirm the death but was offering consular assistance to the family.
"The Australian Government remains deeply concerned about the situation of Australians in northeast Syria, including the welfare of those detained in prisons and other detention centres'', a department spokeswoman said in a statement.