GENEVA, Switzerland — A United Nations investigation concluded on Wednesday that Israel has committed crimes against humanity during the war in Gaza, including that of "extermination," while saying that Israeli and Palestinian armed groups have both committed war crimes.

The independent Commission of Inquiry's report is the global organization's first in-depth investigation into the events of the war that began on Oct. 7, 2023.

It found that Israel had committed war crimes, crimes against humanity, and violations of international humanitarian law (IHL) and international human rights law (IHRL).

The report noted "a widespread or systematic attack directed against the civilian population in Gaza."

"The commission found that the crimes against humanity of extermination; murder; gender persecution targeting Palestinian men and boys; forcible transfer; and torture and inhuman and cruel treatment were committed," it said.

Israel rejected the conclusions by accusing the UN commission of "systematic anti-Israeli discrimination."

The war broke out after Hamas' unprecedented attacks on southern Israel resulted in the deaths of 1,194 people, mostly civilians, an Agence France-Presse (AFP) tally based on Israeli official figures shows.

The commission found that in that attack, members of the military wings of Hamas and other Palestinian armed groups and Palestinian civilians committed war crimes, as well as violations and abuses of IHL and IHRL.

Militants seized 251 hostages, of which 116 remain in Gaza, though the Israeli army says 41 of them are dead.

In response, the Israeli army launched a devastating offensive on the Gaza Strip that has left more than 37,000 people dead, the majority of them civilians, the Hamas-ruled territory's Health Ministry said.

The Commission of Inquiry was established by the UN Human Rights Council in May 2021 to investigate alleged violations of IHL and IHRL in Israel and the Palestinian territories.

Since October 7, the three-member commission has focused on the war between Israel and Hamas.

"It is imperative that all those who have committed crimes be held accountable," said the commission's chairman Navi Pillay, a former UN rights chief and an ex-International Criminal Court judge.

"Israel must immediately stop its military operations and attacks in Gaza," she said. "Hamas and Palestinian armed groups must immediately cease rocket attacks and release all hostages. The taking of hostages constitutes a war crime."

'War crimes' in October attack

The commission concluded that members of Hamas, other Palestinian armed groups and civilians participating in the October 7 attacks "deliberately killed, injured, mistreated, took hostages and committed sexual and gender-based violence."

These acts were committed against civilians and members of the Israeli security forces.

"These actions constitute war crimes and violations and abuses of IHL and IHRL," it said.

The commission further said it found "significant evidence on the desecration of corpses, including sexualized desecration, decapitations, lacerations, burning, severing of body parts and undressing."

"Women were subjected to gender-based violence during the course of their execution or abduction. Women and women's bodies were used as victory trophies by male perpetrators."

Many children who witnessed their relatives being killed were "also filmed for propaganda purposes," with the commission finding it "particularly egregious that children were targeted for abduction."

The report said Israeli authorities "failed to protect civilians in southern Israel on almost every front."

Israel's 'starvation' of Gaza

In their actions in Gaza, the commission found the Israeli authorities "responsible for the war crimes of starvation as a method of warfare, murder or willful killing, intentionally directing attacks against civilians and civilian objects, forcible transfer, sexual violence, torture and inhuman or cruel treatment, arbitrary detention and outrages upon personal dignity."

Starvation will affect the Gaza population, particularly children, "for decades to come," the report said, while "the siege it imposed... constitutes collective punishment and reprisal against the civilian population, both of which are clear violations of IHL."

The report is based on interviews with victims and witnesses conducted remotely, and in Turkey and Egypt, and through studying thousands of verified open-source items, satellite imagery and forensic medical reports, the commission said.

The report is due to be presented to the UN Human Rights Council next week.