The UN human rights chief says Israel used "wholly disproportionate" force against Palestinian border protests which have left over 100 people dead.
Zeid Raad al-Hussein told a meeting in Geneva that Gazans were effectively "caged in a toxic slum" and Gaza's occupation by Israel had to end.
Israel's ambassador said Gaza's militant Islamist rulers had deliberately put people in harm's way.
The UN's Human Rights Council voted to set up an independent investigation.
Some 60 Palestinians were killed by Israeli forces on Monday in the seventh consecutive week of border protests, largely orchestrated by Hamas, which politically controls the Gaza Strip.
It was the deadliest day in Gaza since a 2014 war between Israel and militants there.