The Commission of Inquiry on the 2014 Gaza conflict announced "it had received credible allegations" that both sides had committed war crimes during the conflict, which killed more than 2,140 Palestinians, most of them civilians, and 73 people on the Israeli side, mostly soldiers.
"The extent of the devastation and human suffering in Gaza was unprecedented and will impact generations to come," said the chair of the commission, New York judge Mary McGowan Davis.
Israel, which has been harshly critical of the commission since its inception last year, blasted the report as biased, with Prime Minister Benjamin Netanyahu insisting his country "does not commit war crimes".
"Israel defends itself against a terror organization which calls for its destruction and that itself carries out war crimes," Netanyahu said in a statement, referring to Islamist movement Hamas, which rules the Gaza Strip.
Hamas meanwhile hailed the report's "condemnation of the Zionist occupier for its war crimes".
The report criticized both sides, but especially decried the "huge firepower" Israel had used in Gaza, with more than 6,000 airstrikes and 50,000 artillery shells fired during the 51-day operation.
551 children killed
The bombings of residential buildings had especially dire consequences, wiping out entire families, with 551 children killed, a choked-up McGowan Davis pointed out to reporters.
Hundreds of Palestinian civilians were killed in their own homes, and the report provided heart-wrenching testimony from a man who lost 19 of his relatives in an attack in Khan Younis on July 26, including his mother and all of his children.
"We all died that day, even those who survived," he said.
According to the report, which will be presented to the UN Human Rights Council on June 29, 742 people were killed in attacks on residential buildings, with at least 142 families losing three or more members.
"The fact that Israel did not revise its practice of air-strikes, even after their dire effects on civilians became apparent, raises questions of whether this was part of a broader policy which was at least tacitly approved at the highest level of government," the commission said in a statement.
The investigators meanwhile also decried the "indiscriminate" firing of thousands of rockets and mortars at Israel, which it said appeared to have been intended to "spread terror" among Israeli civilians.
Palestinian armed groups fired 4,881 rockets and 1,753 mortars towards Israel, killing six civilians and injuring at least 1,600 others, it pointed out.
McGowan Davis said one Israeli woman had described the helplessness she felt when her grandchild pleaded with her to "stop the rockets".
The two-member commission also pointed out that tunnels dug by Palestinian militants into Israel had traumatized Israeli civilians "who feared they could be attacked at any moment by gunmen bursting out of the ground".
Failure to achieve justice
While the conflict has ended, McGowan Davis pointed to a "pervasive failure on all sides to achieve justice" for the wrongs committed, and the investigators urged Israel to "break with its recent lamentable track record in holding wrongdoers accountable".
They were not granted entry to Israel or the conflict area, and relied instead on more than 280 confidential interviews and some 500 written submissions for their findings.
The report, initially scheduled for publication in March, was delayed after the head of the team quit under Israeli pressure.
Canadian international law expert William Schabas resigned as chair of the commission after Israel charged he was biased because he had prepared a legal opinion for the Palestine Liberation Organization (PLO) in October 2012.
Israel was not satisfied, calling for the entire inquiry to be shelved, insisting the commission and the Human Rights Council which created it are inherently biased against the Jewish state.
In the occupied West Bank, a senior PLO official said the report reinforces "our will to go to the International Criminal Court".
Palestinians have been seeking to open criminal proceedings against Israel at the ICC as part of an increased focus on diplomatic maneuvering and appeals to international bodies.
The UN investigators refused to say Monday whether they thought the ICC was an appropriate forum for ensuring accountability for the abuses committed during the 2014 Gaza conflict.
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