• Prof Ruth Halperin-Kaddari said she saw footage of women in several locations whose condition left her in "no doubt" that they had been raped.
• There has been anger over the delay of some UN bodies to acknowledge claims of Hamas's sexual atrocities on 7 October.
Hamas had a premeditated plan to use sexual violence as a weapon of war, an Israeli women's rights campaigner and lawyer has said.
Prof Ruth Halperin-Kaddari said she saw footage of women in several locations whose condition left her in "no doubt" that they had been raped.
There has been anger over the delay of some UN bodies to acknowledge claims of Hamas's sexual atrocities on 7 October.
Israel has been exploring evidence of sexual crimes during the attacks.
Warning: This article contains graphic details which some readers may find upsetting
The scale of sexual violence carried out by Hamas during the October attacks is not yet clear, but Israeli police say they have so far gathered more than 1,500 testimonies from witnesses and medics.
Pictures and live footage streamed by the militants pointed to the gruesome nature of the attacks at the Supernova festival.
A range of violence from gang rape to the sexual mutilation of murdered victims are being investigated by police.
"I saw a number of first-hand, eyewitness accounts, for example of one survivor who hid in the bushes and saw a woman next to her being raped by several men," Prof Halperin-Kaddari told BBC Radio 4's Today programme.
She said she also spoke to a paramedic who treated a woman who lost a life-threatening amount of blood after reporting being raped by four men.
"I saw footage and pictures from numerous locations of bodies whose condition were all exhibiting the same pattern of mutilation and leaving no doubt that rape was performed on these women before they were executed," she said.
"This leaves no doubt that such a concentration of cases in a relatively short span of time - less than a day - in numerous locations, it could not have been unless there had there not been a plan, premeditation, to use sexual violence as a weapon of war."
Hamas denies these abuses. One official, Basem Naim, told The Washington Post that the group considers "any sexual relationship or activity outside of marriage to be completely haram" - forbidden by Islam.
Israeli women's rights and legal activists had been calling on key international organisations to publicly acknowledge reports of gender-based violence, including sexual violence, in the wake of Hamas's attacks.
Prof Halperin-Kaddari, who spent 12 years as a member of a UN convention on discrimination against women, said she and others have been calling on UN bodies to acknowledge these "crimes against humanity".
"Regrettably, until a week ago, none of them said the explicit word 'sexual violence'. It took them more than seven weeks," she said. The UN has yet to respond to accusations of a delay, but Prof Halperin-Kaddari visited the UN in Geneva just a week ago to draw attention to the violence.
UN Women issued a statement - eight weeks after the attacks - acknowledging accounts of gender-based atrocities.
"This took them too long, much too long," Prof Halperin-Kaddari added.
Yael Sherer from the Survivors of Sexual Violence advocacy group told Today that men were also victims of sexual violence on 7 October.
She said evidence is being gathered from some survivors of the attacks, as well as eyewitnesses and first responders, who have been detailing the violence.
"Hamas terrorists made sure to disgrace these people and dishonour them in many ways," she said.
This included violence after the victims were dead, kidnap, abuse and people of many ages bleeding and being tied to furniture with zip ties, she said.
An ongoing UN commission of inquiry investigating war crimes on both sides of the Israel-Hamas conflict will include a focus on sexual violence carried out during the attacks on 7 October. However, Israel has never so far cooperated with the commission, viewing it as biased.
The Hamas attack on Israel on 7 October killed 1,200 people, with around 240 others taken hostage.
Since then, Gaza's Hamas-run health ministry says more than 15,500 people have been killed in Israel's military campaign which it launched in response.