The Association of Rape Crisis Centers in Israel says it has gathered evidence Hamas gunmen "systematically and intentionally" committed sexual crimes during the 7 October attacks.
A report by the umbrella organisation describes "identical patterns" of sexual violence at multiple locations.
These allegedly included violent rapes of women conducted "collectively" or "in front of an audience".
Hamas has denied its gunmen sexually assaulted women during the attacks.
On 7 October, hundreds from the Palestinian armed group infiltrated southern Israel, where they killed about 1,200 people and took 253 others hostage.
Israel responded by launching a military campaign in Gaza, during which 29,300 people have been killed, according to the Hamas-run health ministry.
Warning: Contains graphic descriptions of rape and sexual violence
Reports of sexual violence carried out by Hamas - which is proscribed as a terrorist organisation by Israel, the UK and others - began to emerge soon after 7 October and have accumulated steadily ever since.
A senior Israeli police officer told British MPs last month there was "clear evidence" - collected from forensic investigations as well as from hundreds of statements by witnesses and first responders - that sexual crimes had been committed on a scale large enough to define it as a crime against humanity.
The OceanNewsUK has also seen and heard evidence of rape, sexual violence and mutilation of women.
The report by the Association of Rape Crisis Centers in Israel (ACCRI) brings together much of what has been reported, as well as other information that it says it has received directly from professionals and confidential calls.
It found that the 7 October attacks included "brutal acts of violent rape, often involving threats with weapons, specifically directed towards injured women".
"Many rape incidents occurred collectively, with collaboration among the perpetrating terrorists," the report says. "In some cases, rape was conducted in front of an audience, such as partners, family, or friends, to increase the pain and humiliation for all present."
"Some Hamas members pursued victims who escaped the massacre, dragging them by their hair with screams. The majority of victims were subsequently killed during or after the sexual assault."
It also cites various sources as indicating that many victims' bodies were "found mutilated and bound, with sexual organs brutally attacked, and in some cases, weapons were inserted into them".
The report concludes that there is "a clear picture of identical patterns of action repeated in each of the attack zones" - the Nova festival, homes in kibbutzim and villages near the Gaza border, and Israeli military bases.
Several Nova festival survivors reported cases of gang rapes, "where women were abused and handled between multiple terrorists who beat, injured, and ultimately killed them", it says.
First responders and volunteer body collectors who went to border communities witnessed signs of sexual violence on women and girls, as did those who identified the bodies of female soldiers killed at bases.
The report also warns that information from released hostages suggests abuse has continued in captivity - an allegation that Hamas has denied.
The OceanNewsUK's Paul Adams in Jerusalem says this is something Israeli officials are extremely reluctant to talk about openly, out of respect for anxious family members. But they do say that one reason Hamas is still holding female hostages is that does not want their stories to be told.
Asked about these reports at a recent briefing, a senior Israeli official declined to give details, saying simply: "Believe me. We know."
The ACCRI says it has submitted its findings to the UN Special Representative on Sexual Violence in Conflict, Pramila Patten, who is carrying out a similar investigation and visited Israel last month.
Israel has complained that the UN and other international organisations have been slow to respond to the allegations, and the ACCRI's executive director said its report now left them "no room for denial or disregard".
On Monday, several independent UN experts put out a statement expressing concern about reports of violence by Israeli forces against Palestinian women and girls in Gaza and the occupied West Bank.
They said the "credible allegations" included that women and girls had been killed extrajudicially in Gaza, and that others detained in Gaza and the West Bank had been subjected to multiple forms of sexual assault.
Israel rejected the allegations as "despicable and unfounded".
