The UN has named and shamed more than 50 nations for failing to repatriate almost 10,000 people, mostly women and children, associated with ISIS who are being held in "sub-human" conditions in camps in north-east Syria.
Britain, the US, France and Sweden are among the nations being criticised by UN rights experts who are urging them to take "immediate" action.
There are 9,462 women and children among the 64,600 people being held in "squalid" conditions at the Al Hol and Roj camps, which are run by Syrian Kurdish authorities. Most of the residents are Iraqis and Syrians.
The UN has listed the 57 nations who have failed to act on what has been dubbed a "list of shame" by Fionnuala Ni Aolain, the UN special rapporteur on protecting human rights.
"The matter is one of extreme urgency," she said.
"The camps hold over 64,000 people, mostly women and children. Many of them are highly vulnerable. Many of them are experiencing a range of human rights concerns that require states to act expediently."
She criticised a rise in "nationality stripping", saying it was unlawful to leave someone stateless.
"These women and children are living in what can only be described as horrific and sub-human conditions," Ms Ni Aolain said.
"The conditions in these camps may reach the threshold of torture, inhuman and degrading treatment under international law."
Some women had been "groomed online" to marry ISIS fighters, while children "had no say in what brought them there", she said.
The UN said last month it had received reports of 12 Syrian and Iraqi nationals being murdered in the first half of January at Al Hol, which holds internal refugees and families of ISIS fighters.
Canada, Finland and Kazakhstan have repatriated some nationals, Ms Ni Aolain said, welcoming a "trickle of returns".
But others, such as the UK, have only repatriated children.
In November, Sweden repatriated four women and nine children, but last week it was revealed one of the women has been charged with war crimes and her children have been taken into care.
The UK has only repatriated a handful of unaccompanied children and orphans from the camps.
It is estimated around 60 British youngsters are in the camps living with their mothers, whom the British government refuses to repatriate.
The Home Office has said there are “legitimate security concerns” about the return of orphans from Syria.
“Returnees, even children, are a security risk,” it previously said. “Our view is that repatriations can only be looked at on a case-by-case basis.”
Last year, former UK schoolgirl and ISIS recruit Shamima Begum challenged the UK's decision to strip her of her British citizenship.
in July, the Court of Appeal unanimously agreed that Begum, now 21, could only appeal fairly and effectively if she was allowed back into Britain.
But the Home Office took the case to the Supreme Court to challenge that decision on the grounds that she still poses a threat to national security and is awaiting the result.
Ms Ni Aolain has compared the "illegal detention" of the Syrian camp detainees to that of security suspects held at the US prison in Guantanamo Bay for years without charge.
"These women and children are a convenient battering ram on all the fears of state and the public," Ms Ni Aolain said. "They are made objects of hate, ridicule and shame."
She said she had conveyed her demands in detailed letters to each country concerned, including Australia, Bangladesh, Belgium, Britain, Canada, China, France, Germany, India, Pakistan, Russia, Switzerland, Turkey, and the United States.
"It is the first time that these 57 states have been named together," said Ms Ni Aolain.
"This isn't a club you want to belong to."
Some 48 per cent of the 64,000 people in the camp are Iraqis, 37 per cent are Syrians and 15 per cent are third-country nationals.
The are the families of ISIS fighters, which seized swathes of Iraq and Syria in 2014. The Iraqi and Syrian residents of the camp largely fled subsequent fighting between ISIS and Kurdish forces.
Last month, the UN's counterterrorism chief, Vladimir Voronkov, told an informal meeting of the UN Security Council that "the horrific situation of the children in Al Hol [camp] is one of the most pressing issues in the world today."
He urged countries to repatriate the 27,000 children stranded in the camp and said they “remain stranded, abandoned to their fate,” vulnerable to being preyed on by ISIS enforcers, “and at risk of radicalisation within the camp".