The UN Human Rights Council has voted to investigate violence in the recent conflict between Israel and Hamas.
The body approved the resolution, brought by a group of Islamic countries, by 24 votes to nine.
But the United States said the decision threatened to endanger progress in bringing calm to the region.
At least 242 people were killed in Gaza and 13 were killed in Israel during 11 days of fierce fighting that ended on Friday with an Egyptian-brokered truce.
The violence came after weeks of spiralling Israeli-Palestinian tension in occupied East Jerusalem which culminated in clashes at a holy site revered by both Muslims and Jews.
Hamas began firing rockets into Israel after warning it to withdraw from the site, triggering retaliatory air strikes from Israel on Gaza targets.
The text of the resolution, brought by the Organisation of Islamic Conference (OIC) and the Palestinian delegation, calls for a permanent Commission of Inquiry to be set up to report on rights violations in Israel, the West Bank and Gaza.
It also calls for the investigation of "all underlying root causes of recurrent tensions, instability and protraction of conflict".
Opening the council session, UN human rights chief Michele Bachelet said she was concerned about the high level of casualties in Gaza and warned that Israeli strikes might constitute war crimes.
She also described Hamas rocket fire at Israel as indiscriminate and a "clear violation" of international humanitarian law.
Nine members, including several Western countries, voted against the resolution and another 14 abstained. China and Russia were among those voting in favour.
The US, which only has observer status at the council, did not take part in the debate.
But its mission to the UN in Geneva released a statement after the vote, saying it deeply regretted the move.
"It is deeply unfortunate that while we and others have been working to uphold and strengthen the ceasefire, ensure humanitarian assistance to Gaza, and continue the hard work of discussions on how to achieve a lasting peace, some members of the Human Rights Council have chosen to engage in a distraction that adds nothing to ongoing diplomatic and humanitarian efforts," the statement said.
"The action today instead threatens to imperil the progress that has been made in recent weeks."
Israeli Prime Minister Benjamin Netanyahu denounced the move as "yet another example of the UN Human Rights Council's blatant anti-Israel obsession".
But the Palestinian foreign ministry said it reflected the "determination of the international community to move forward in the path of accountability, law enforcement, and protection of Palestinian human rights".
Hamas, meanwhile, called for "immediate steps to punish" Israel.
The vote came after US Secretary of State Antony Blinken finished a three-day tour of the Middle East.
On Tuesday he visited the West Bank, calling for the ceasefire to be strengthened and promising aid for rebuilding Gaza.
He said the US was working with the international community, the Palestinian Authority and Israel to help in the relief and recovery efforts in Gaza, including $5.5m (£3.9m) in immediate disaster assistance.
Earlier Mr Blinken reaffirmed the US's "ironclad commitment" to Israel's security.