In a report after spending about two weeks in Israel and the West Bank with a team of nine people, Pramila Patten concluded there are also "reasonable grounds to believe that such violence may be ongoing".

She said the team had "found clear and convincing information" that some hostages have been subjected to the same forms of conflict-related sexual violence including rape and "sexualised torture".

Hamas has previously rejected allegations that its fighters committed sexual assault.

Warning: Article contains details of violence that some readers may find distressing

Ms Patten and her team visited Israel and the West Bank from 29 January to 14 February for a visit aimed at gathering and analysing information on possible sexual violence during the attacks.

They were not able to meet with any victims of sexual violence "despite concerted efforts to encourage them to come forward," said Ms Patten, the UN envoy focusing on sexual violence in conflict.

However, team members held more than 30 meetings with Israeli institutions, and carried out interviews with 34 people including survivors and witnesses of the attacks, hostages who have since been released, health officials and others.

Middle East latest: Israel makes new claim about UN agency

The team gathered "credible circumstantial information, which may be indicative of some forms of sexual violence, including genital mutilation, sexualised torture, or cruel, inhuman and degrading treatment", said the 24-page report.

It said "there are reasonable grounds to believe that conflict-related sexual violence occurred during the 7 October attacks in multiple locations across Gaza periphery, including rape and gang rape, in at least three locations".

The team said "several fully naked or partially naked bodies from the waist down were recovered - mostly women - with hands tied and shot multiple times, often in the head".

One of the locations mentioned was the Nova music festival and its surroundings, where "multiple incidents of sexual violence" may have taken place, "with victims being subjected to rape and/or gang rape and then killed or killed while being raped".

The team said the visit "was neither intended nor mandated to be investigative in nature" and stressed a "fully-fledged investigation" would be required to establish the overall magnitude, scope and specific attribution for the sexual violence.

Read more from Sky News:
Why this week could be critical for Gaza
A fresh Israel-Hamas truce could be highly significant
'I won't forget them,' says brother of twins held in Gaza

At Kibbutz Be'eri, Ms Patten said her team "was able to determine that at least two allegations of sexual violence widely repeated in the media, were unfounded due to either new superseding information or inconsistency in the facts gathered".

The Hamas attacks left 1,200 people dead and about 250 others taken hostage.

Israel's war against Hamas has since left 30,000 dead in the Gaza Strip, according to Gaza's Hamas-run Health Ministry.

A quarter of Gaza's 2.3 million people face starvation, according to the UN.