They said the cases they had documented probably amounted to violations of international humanitarian law and called for coalition members to create a fund to compensate victims and their families.
Daesh seized Raqqa in early 2014 during its lightning advance through Syria and Iraq in which it built a self-proclaimed caliphate characterised by summary killings of opponents. The group, which controlled a third of both Syria and Iraq in 2014, has since been driven from all the territory it controlled by military campaigns waged by an array of enemies including the Syrian and Iraqi governments, the United States, its European allies and their rivals Russia and Iran.
The YPG is the Syrian extension of the PKK, which is designated as a terror organisation by Turkey, the US and the EU.