The U.N. human rights office said on Tuesday the killingsof civilians in Gaza during the Israeli operation to release four hostages, and also armed groups’ holding of captives in densely populated areas, could amount to war crimes.

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

The operation killed more than 270 Palestinians, according to Gazan health officials.

“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,” Jeremy Laurence, spokesperson for the U.N. human rights office, said.

Laurence added that the holding of hostages in such densely populated areas by armed 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 in Gaza was triggered when Hamas fighters charged into Israel on Oct. 7 and killed some 1,200 people, according to Israeli tallies. Israel’s subsequent bombardment and invasion of Gaza has killed more than 37,000 Palestinians, according to health authorities in the Hamas-run enclave.

Gunmen took around 250 hostages back to Gaza on Oct. 7, more than 100 of whom were released in exchange for about 240 Palestinians held in Israeli jails during a week-long truce in November.

There are 116 hostages left in the coastal enclave, according to Israeli tallies, including at least 40 whom Israeli authorities have declared dead in absentia.