Navi Pillay, U.N. high commissioner for human rights, referred to reports of executions in the first week of January conducted by Islamic State of Iraq and Syria, an insurgent group loyal to al-Qaida.
A United Nations statement Thursday mentioned numerous individuals executed in Idlib by armed groups, three handcuffed people found dead by bullet wounds through their heads in Makfar al-Saleheen, and numerous handcuffed and blindfolded bodies found at a Children's hospital in Aleppo formerly used as an ISIS headquarters.
"We have received reports of a succession of mass executions of civilians and fighters who were no longer participating in hostilities," Pillay said. "While exact numbers are difficult to verify, reliable eyewitness testimony ... suggests many civilians and fighters in the custody of armed extremist groups have been executed."
She warned executions and unlawful killings are in violation of international law and may be treated as war crimes.