The call from the United Nations High Commissioner for Human Rights, Michelle Bachelet, came as world leaders face divisive decisions over the families of foreign jihadists captured or killed in Syria and Iraq.

Australia on Monday confirmed that eight orphans of Australian IS fighters had been spirited out of a camp in Syria and were now under the government's care.

The move marked a U-turn for Prime Minister Scott Morrison, who had previously indicated his government would only help citizens if they approached an embassy or consulate.

Morrison said Australia's decision to assume care of the eight children -- believed to be aged between two and 17 -- was not "made lightly". But ultimately he concluded "children should not be punished for the crimes of their parents".

Following the collapse of IS's self-proclaimed caliphate, foreigners from nearly 50 countries have been detained in Syria and Iraq, and more than 11,000 of their family members are being held in difficult conditions in Syria's al-Hol camp.

In a speech to the opening session of the UN Human Rights Council, Bachelet sought to provide clarity to governments uncertain how to handle the families -- and especially children -- of jihadist fighters from their country.

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

"Children, in particular, have suffered grievous violations of their rights, including those who may have been indoctrinated or recruited by ISIL to perpetrate violent acts," she said, using another acronym for IS.

"The primary consideration must be their rehabilitation, protection and best interests."

The UN rights chief pointed to UNICEF estimates that there are some 29,000 children of foreign fighters in Syria -- 20,000 of them from Iraq -- and most of them under 12.

France, which has one of the largest contingents of jihadists who were captured or turned themselves in, took in 12 children of French jihadists earlier this month.

Paris has said it is studying the files of all its citizens held in northeastern Syria on a case-by-case basis.

- 'Irresponsible cruelty' -

Many of the children were born in Syria, and some governments have refused to grant them their parent's nationality.

"Despite the complexity of these challenges, rendering people stateless is never an acceptable option," Bachelet said.

"Thousands of young children have been born to foreign families during the years of conflict, and states should provide the same access to nationality for children born to their nationals in conflict zones as is otherwise applicable," she said.

"To inflict statelessness on children who have already suffered so much is an act of irresponsible cruelty," she insisted.

Bachelet also stressed that countries remained responsible for their citizens facing prosecution for being foreign fighters in Syria, as well as in Iraq, where more than 150 have been sentenced to death under anti-terrorism laws.

"States have important responsibilities for their own nationals," including ensuring they receive fair trials, she said.

- Sudan request -

Separately, Bachelet voiced deep concern over Sudan, which has been wracked by tensions between protesters and the generals who seized power after the army ousted long-time president Omar al-Bashir in April.

Bachelet cited reports that more than 100 people were killed and many more injured in a breakup of a peaceful June 3 rally.

"We have received allegations of rape and sexual abuse of both women and men during the crackdown, as well as information alleging that hundreds of protestors may be missing," she said.

"I regret that the government has not responded to our request for access to investigate allegations of serious human rights violations by the joint security forces during the crackdown," she added.

Bachelet also called for Sudan to end a nationwide internet blockade.