As reported by Censor.NET citing Al Jazeera, Zeid Ra'ad al Hussein's comments on Friday came during a special session of the UN human rights council called by Britain to set up a special inquiry into violations, especially in Aleppo's rebel-held east where an estimated 275,000 civilians are besieged by a Syrian government offensive backed by Russia.
In a video speech, Zeid said Aleppo is a "slaughterhouse" and called for major powers to put aside their differences and refer the situation in Syria to the prosecutor of the International Criminal Court (ICC).
Earlier this week, the European Union strongly condemned Russia and the Syrian government for causing "untold suffering" and suggested their actions in the city may amount to "war crimes".
"The deliberate targeting of hospitals, medical personnel, schools and essential infrastructure, as well as the use of barrel bombs, cluster bombs, and chemical weapons, constitute a catastrophic escalation of the conflict... and may amount to war crimes," European Union foreign ministers said in a joint statement.
On Monday, France announced that it would ask the ICC to investigate possible war crimes committed in Aleppo.
British Foreign Secretary Boris Johnson also gave his backing to French calls for an ICC investigation into alleged war crimes in the city.
Later on Friday, the UN said medical evacuations from eastern Aleppo had not begun on Friday as it had hoped, as a lack of security guarantees and "facilitation" prevent aid workers taking advantage of the pause in the bombing announced by Russia.
Related materials: War in Syria