As reports continued to emerge of a succession of mass executions in northern Syria, UN High Commissioner for Human Rights Navi Pillay on Thursday warned armed opposition groups that executions and unlawful killings are in violation of international human rights and humanitarian law and may amount to war crimes.

“In the past two weeks, we have received reports of a succession of mass executions of civilians and fighters who were no longer participating in hostilities in Aleppo, Idlib and Raqqa by hardline armed opposition groups in Syria, in particular by the Islamic State of Iraq and Syria (ISIS),” the High Commissioner said.