The Israeli killing of hundreds of Palestinians in a military raid to recover four hostages from Gaza over the weekend may have amounted to war crimes, the U.N. human rights office (OHCHR) said Tuesday.

The OHCHR accused the Palestinian resistance groups of the same crime for holding captives in densely populated areas.

Israel claimed the operation, accompanied by an air assault, took place Saturday in the heart of a residential neighborhood in central Gaza's Nuseirat area where Hamas had kept the hostages in two separate apartment blocks.

The operation killed at least 274 Palestinians, according to Gazan health officials.

"We are profoundly shocked at the impact on civilians of the Israeli forces' operation in An Nuseirat at the weekend to secure the release of four hostages," spokesperson Jeremy Laurence told reporters in Geneva.

"Hundreds of Palestinians, many of them civilians, were reportedly killed and injured."

"The manner in which the raid was conducted in such a densely populated area seriously calls into question whether the principles of distinction, proportionality and precaution – as set out under the laws of war – were respected by the Israeli forces," Laurence said.

Asked about figures provided by the Gaza Health Ministry, he said that prior to Oct. 7, when there was greater possibility to check, the U.N. had consistently found "the numbers they provide us are ... very close to being 100% accurate."

The U.N. rights office has had limited access to verify numbers since the war started but Laurence said it still had contacts on the ground "who are reliable."

Asked about hostages held in Gaza, Laurence said this was also "prohibited by international law."

He added that the holding of hostages in such densely populated areas by the Palestinian groups was "putting the lives of Palestinian civilians, as well as the hostages themselves, at added risk from the hostilities."

"All these actions, by both parties, may amount to war crimes," he said.

The conflict was triggered by the Oct. 7 Hamas incursion, which resulted in the death of more than 1,170 people in Israel, according to official Israeli figures.

Out of 252 people taken hostage that day, 120 are still being held inside the Gaza Strip, including at least 43 who the army says are dead.

Israel has killed over 37,000 Palestinians, mostly women and children, in the Gaza Strip since, according to the Gazan Health Ministry.