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 meeting is considering calling for an independent investigation.
Some 60 Palestinians were killed by Israeli forces on Monday on 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.
The protests had been dubbed the Great March of Return, in support of the right of Palestinian refugees to return to land they or their ancestors fled from or were forced to leave in the war which followed Israel’s founding in 1948.
The Israeli government, which has long ruled out a mass return of Palestinians, said terrorists wanted to use the protests as cover to cross into its territory and carry out attacks.
Mr Zeid told the emergency session on Gaza that the “stark contrast in casualties on both sides is… suggestive of a wholly disproportionate response” by Israel.
An Israeli soldier was “reportedly wounded, slightly, by a stone” on Monday, he said, while 43 Palestinians were killed at the site of the protests. Seventeen more Palestinians were killed away from what he called the “hot spots”.
He said there had been “little evidence of any [Israeli] attempt to minimise casualties”. Israel’s actions might, he said, “constitute ‘wilful killings’ – a grave breach of the Fourth Geneva Convention”, an international law designed to protect civilians under occupation.
Mr Zeid said he supported a call for an “international, independent and impartial” investigation into the violence in Gaza, adding that “those responsible for violations must in the end be held accountable”.
Israel’s Ambassador Aviva Raz Shechter rejected the blame, saying Israel had done everything possible to avoid harming civilians.
She said the UN Human Rights Council had returned to its “worst form of anti-Israel obsession”.
“This special session, the resolution before you, and its call for a commission of inquiry are yet again politically motivated and won’t change the situation on the ground by even one iota,” she said.
Tens of thousands of Palestinians have held weekly protests at the border in the lead-up to the 15 May anniversary of the mass displacement of Palestinians from land which became Israel in the war which followed Israel’s founding in 1948.
While most Palestinians have demonstrated at a distance from the heavily guarded fence, Israel said its soldiers only used lethal force against people carrying out “terrorist activity and not on demonstrators”.