The UN voiced alarm on Tuesday at the high Palestinian death toll following Israel's attack on the Nuseirat camp, used to rescue four Israeli captives, and at Palestinian armed groups are holding captives there.
The United Nations rights office (OHCHR) said acts committed by both Israelis and Hamas "may amount to war crimes".
"We are profoundly shocked at the impact on civilians of the Israeli forces' operation in Nuseirat at the weekend to secure the release of four hostages," spokesman Jeremy Laurence told reporters in Geneva.
The UN, he said, was also "deeply distressed that Palestinian armed groups continue to hold many hostages, most of them civilians".
Israeli forces stormed Nuseirat refugee camp on Saturday to rescue four Israeli hostages, killing at least 274 Palestinians and 698 wounded during the operation that triggered global outrage.
"Hundreds of Palestinians, many of them civilians, were reportedly killed and injured," Laurence said.
"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."
Asked about figures provided by the Gaza health ministry, he said that prior to October 7, when there was greater possibility to check, the UN had consistently found "the numbers they provide us are very close to being 100-percent accurate".
The UN 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".
"Furthermore, by holding hostages in such densely populated areas, the armed groups doing so are putting the lives of Palestinian civilians, as well as the hostages themselves, at added risk from the hostilities," he stressed.
Israel's relentless bombing and ground offensive in Gaza has killed at least 37,164 people there, mostly women and children, while thousands are feared to be trapped under rubble.