Michelle Bachelet says children in particular have suffered ‘grievous violations’ of their rights.

Thousands of relatives of suspected ISIL fighters should be taken back by their countries of origin, the United Nations human rights chief has said.

Speaking at the UN Human Rights Council as it opened its annual summer session in Geneva, Michelle Bachelet said on Monday that children, in particular, had suffered “grievous violations” of their rights.

“Foreign family members should be repatriated, unless they are to be prosecuted for crimes in accordance with international standards,” she said.

The UN Children’s Fund (UNICEF) estimates that there are 29,000 children of foreign fighters in Syria, of which 20,000 are from Iraq.

In total, more than 55,000 suspected ISIL fighters and their families have been detained in Syria and Iraq following the armed group’s collapse. Most of them are citizens of these two countries, but overall the suspected ISIL fighters come from nearly 50 countries, Bachelet said.

More than 11,000 of their relatives are being held at the Al Hol camp in northeastern Syria alone, she added, noting that many there lived in “deeply sub-standard” conditions.

Bachelet appealed to the relevant countries to uphold their responsibilities under international law – even with regard to members of an armed group infamous for beheadings and other grave violence.

“Regarding the alleged fighters, well over 150 men and women have been sentenced to death in Iraq under the anti-terrorism law, following trials which have not afforded adequate due process guarantees,” Bachelet said.

Putting European fighters on trial in their home countries is considered problematic, as little evidence that would survive judicial scrutiny directly links them to crimes in Syria and Iraq.

The US has been urging European countries to bring back their nationals and put them on trial – but most EU countries have refused. Russia and Kazakhstan have been most active at repatriating foreign fighters and their families.

Earlier on Monday, Australian Prime Minister Scott Morrison said eight children of two slain ISIL fighters had been removed from Syria to an unspecified location before planned repatriation to Australia. It would mark the country’s first organised repatriation from the area.

Groups of French children were returned to France earlier this month, along with at least three adults who were immediately detained for questioning. A dozen French people have been sentenced to death in Iraq.

There has been a recent push for an international tribunal to try former ISIL fighters, but it has yet to gain tangible backing.

In her wide-ranging speech, Bachelet also expressed “regret” at Saudi Arabia‘s “dismissal” of a report last week by an independent UN human rights expert criticising the kingdom over the killing of Saudi journalist Jamal Khashoggi.

Separately, she commended a “sound decision” by Hong Kong authorities to delay a bill on extradition that fanned mass protests.