Wednesday's comments from Michelle Bachelet, a former Chilean president, came during her first annual address to the Human Rights Council since becoming the UN High Commissioner for Human Rights in September.
She lamented that Israel responded to a report published Monday on the Gaza violence "without addressing any of the serious issues raised."
Bachelet made "gross inequalities" in the world a major theme in her speech.
The report commissioned by the council found Israeli soldiers intentionally fired on civilians and could have committed crimes against humanity in crackdowns that killed 189 people and left 6,000 hurt by sniper fire.
The goverment called the report "hostile, false and biased," while Prime Minister Benjamin Netanyahu said the report reflected the council's "obsessive hatred" of Israel.
"The UN Human Rights Council is setting new records of hypocrisy and lies stemming from its obsessive hatred toward Israel, the only democracy in the Middle East. Hamas is the one firing missiles at Israeli civilians, throwing explosive devices and carrying terrorist activity during demonstrations on the Gaza border," Netanyahu said.