Human Rights Watch (HRW) in a report released Wednesday raised concerns over the forcible recruitment of children into a youth group associated with the Syrian Democratic Forces (SDF).

HRW interviewed multiple families whose children were taken by the Revolutionary Youth Movement of Syria, or Tevgera Ciwanên Şoreşger. The report revealed that in the vast majority of cases, the families’ teenage son or daughter “simply left home one day, and never returned.” In some instances, parents were able to locate their children by contacting local militia forces, who sometimes confirmed the presence of their children in the SDF youth group. Investigations revealed that members of the SDF often recruited children via social media or phone. Typically, recruitment took place by promising youth educational, cultural or vocational opportunities, constituting “covert recruitment.”

Responding to the allegations, the SDF noted that it has returned children to their parents on multiple occasions when asked, and emphasized that youth enlistments are voluntary. The SDF had previously signed an agreement with the United Nations against child recruitment, and US State Department reports document punitive action taken against militants that have violated this commitment.

Recruitment of children under 15 into armed conflict is considered a war crime under section 8(b)(xxvi) of the Rome Statute, an international treaty governing war crimes prosecuted by the International Criminal Court. Recruiting children under 15 into armed forces also violates section 38 of the United Nations Convention on the Rights of the Child.

The Revolutionary Youth Movement of Syria is ideologically aligned with Kurdish independence movements such as the Kurdistan Workers Party (PKK) and Democratic Union Party (PYD), which broadly follow the ideology of imprisoned PKK leader Abdullah Öcalan. The PYD-affiliated SDF took control over large parts of northeastern Syria after the eruption of the Syrian civil war created a power vacuum, as the ruling Bashar Assad regime battled various rebel groups, the SDF, and ISIS. During the conflict, the SDF have been the recipient of large quantities of military and financial aid by the US to limit the influence of the Islamic State in the region.