Gazans detained by Israeli forces are coming back "completely traumatized" upon release and reporting abuses while in captivity, the head of the UN's Palestinian refugee agency said Monday.

Detainees reported being subjected to a "broad range of ill treatment" including threats of electrocution, being photographed naked, sleep deprivation and having dogs used to intimidate them, UNRWA chief Philippe Lazzarini told a media briefing.

The comments follow reporting by the New York Times on an internal investigation compiled by UNRWA staff documenting the state of returning detainees at the Kerem Shalom border.

"We have seen these people coming back from detention, some of them for a couple of weeks, some of them for a couple of months, and most of them coming back (are) completely traumatized by the ordeal they have gone through," Lazzarini said.

"A number of people have been... debriefed about their ordeal, and we have indeed (compiled) an internal report about their experiences."

The report had been shared with rights groups specializing in detention, he added.

Lazzarini's comments capped a tumultuous day during which Israel and UNRWA have traded accusations, with Israel accusing the agency of having employed more than 450 "terrorists."

Israel also recalled its ambassador to the UN for consultations after the country accused the organization of failing to adequately address claims of sexual violence against Israelis committed by Hamas during the October 7 attacks.

A UN report issued Monday said that there were "reasonable grounds to believe" rapes were committed in Hamas' attack, and that hostages subsequently taken to Gaza have also been raped.

Ahead of Lazzarini's comments, meanwhile, UNRWA said Israeli authorities had "detained several of its staff from the Gaza Strip," who later described abuses in custody.

"Our staff have reported atrocious events while they were detained and during interrogations by the Israeli authorities. These reports included torture, severe ill-treatment, abuse and sexual exploitation," UNRWA said in a statement to AFP.

"Some of our staff have conveyed to UNRWA teams that they were forced to sign confessions under torture and ill-treatment" while being asked about Hamas's October 7 attack.

The "IDF denies general and unsubstantiated claims regarding sexual abuse of detainees in the IDF's detention facilities," the Israeli military said in a statement, using the abbreviation for the Israeli Defense Forces.

The Hamas attack on southern Israel resulted in about 1,160 deaths, most of them civilians, according to an AFP tally based on official Israeli figures.

Israel's retaliatory offensive in Gaza has killed 30,534 people, mostly women and children, according to the latest toll from Hamas-run Gaza health ministry.

Around 250 hostages were taken by militants, 130 of whom remain in Gaza, including 31 presumed dead, according to Israel.