“And the continuing detention of individuals not suspected of crimes, in the absence of lawful basis and regular independent judicial review, is not acceptable.”

Michelle Bachelet, the chief of the United Nations Commission for Human Rights (UNCHR), told a UNCHR conference held Monday in Geneva that at least 55,000 ISIS fighters are in custody in Iraq and Syria, along with their family members. She called for all detainees to face a trial or be let go and for family members to be repatriated or charged with a crime.

“It must be clear that all individuals who are suspected of crimes — whatever their country of origin, and whatever the nature of the crime — should face investigation and prosecution, with due process guarantees,” said Bachelet.

“And the continuing detention of individuals not suspected of crimes, in the absence of lawful basis and regular independent judicial review, is not acceptable,” Bachelet added. She also warned that flawed trials “can only serve the narrative of grievance and revenge.”

The UNCHR said that there are currently 29,000 children of killed and detained militants who belong to the Islamic State in Syria and Iraq militant group, known as ISIS.

The UN rights chief’s data comes from the U.N. Children’s Fund (UNICEF) estimates that of the 29,000 children of foreign fighters in Syria, 20,000 of which are from Iraq.

Bachelet called for the return of the 29,000 children of ISIS militants to their home countries.

“Foreign family members should be repatriated, unless they are to be prosecuted for crimes in accordance with international standards,” Bachelet told the Geneva conference.

Bachelet urged countries to look into the fate of the children of foreign ISIS militants who were born during the years of conflict. She called for granting nationalities to the children and warned of the dangers of rendering children stateless.

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

“To inflict statelessness on children who have already suffered so much is an act of irresponsible cruelty,” Bachelet warned.

Western Countries Reluctant to Repatriate ISIS Militants

Bachelet’s message comes as many western countries to which ISIS members belong refuse to repatriate militants and their family members detained by the Syrian Democratic Forces.

“Following the collapse of ISIS’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 Syria’s al-Hol camp ‘in deeply sub-standard conditions,'” Bachelet said.

Most western countries are afraid of holding trials on their home soil for their citizens who joined ISIS. The countries contend that such tribunals could pose high-security risks at home.

In one high profile example, the U.K. stripped citizenship from a woman named Shamima Begum. Begum left the U.K. when she was 15 and joined the Islamic State in Syria with two friends. She said she wanted to return to the U.K. but was denied permission to repatriate and is being detained in the al-Hol camp in northern Syria, where three of her children died.

According to NPR, the U.S. has returned three American women and 10 children from northern Syria and a State Department spokesperson has said that “appeals [lodged] by alleged American citizens to return to the U.S. are being looked at on a case-by-case basis.”