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An elderly Jewish man attending a pro-Israel rally in California has died after a "physical altercation" with a pro-Palestinian protester, the Ventura County Sheriff's Department announced on Monday evening.

Deputies responded to reports of a battery at a demonstration on Westlake and Thousand Oaks Boulevards after a verbal altercation broke out between 69-year-old Paul Kessler and an unnamed protester on Sunday afternoon, per a department press release. 

"Witness accounts indicated that Kessler was involved in a physical altercation with [pro-Palestinian] counterprotesters," the release continued. "During the altercation, Kessler fell backwards and struck his head on the ground."

The department said it is continuing to investigate the incident and the "possibility of a hate crime" has not been ruled out.

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Paul Kessler holding Israel flag

(Paul Kessler, 69, (pictured) was killed after an altercation broke out with an unnamed pro-Palestinian protester in Ventura County, California, on Sunday. (Provided to Fox News Digital))

Kessler's autopsy at the Ventura County Medical Examiner's Office determined the cause of death to be blunt force head injury and the manner of death to be homicide, per the release.

The department is requesting that anyone who witnessed or captured footage of the incident call Detective Stump at (805) 384-4745.

Video posted online shows Kessler on the ground bleeding and holding his head. A protester holding a "Free Palestine" sign and wearing a Palestinian flag embroidered on her jacket could be seen leaning over him.

A local man who was at the protest met Kessler minutes before he died, though he did not witness the altercation. The man, who did not want to be named, shared with Fox News Digital that he left to get something from his car and, when he returned, he saw Kessler "lying on the ground with blood everywhere."

Paul Kessler lies on the ground after being struck in the head

Kessler died after falling backwards and hitting his head during an altercation with a pro-Palestinian protester, according to the Ventura County Sheriff's Office. The Jewish Federation of Greater Los Angeles said a megaphone was thrown at Kessler. (Provided to Fox News Digital)

Multiple onlookers dialed 911 but were unable to get through, including the alleged perpetrator, the man shared.

He said Kessler "was out," but had "moments where he lifted his head, touched the back of his head [and] lifted his legs up."

"He took a very hard jar to the back of his head. His brain must’ve [been] swollen," the man told Fox News Digital.

Los Angeles Mayor Karen Bass issued a statement mourning Kessler's death. 

"We mourn the death of the Jewish man who died after being injured during a protest in Thousand Oaks. As details emerge and are confirmed, we stand resolute in condemnation of violence and antisemitism," Bass said. "This death is a blow to our region at a time when tensions continue to rise worldwide. We must redouble our efforts to ensure violence and hate are met with accountability and consequences. Los Angeles refuses to harbor this hatred."

The Jewish Federation of Greater Los Angeles wrote in a post on X Monday evening that the pro-Palestinian protester threw a megaphone at Kessler.

The man who didn't want to be identified described some of the pro-Palestinian protesters as "extremely aggressive" and said they were yelling at police and "trying to incite a reaction or response."

The pro-Palestinian protesters could also be heard shouting "Allahu Akbar" in a video shared with Fox News Digital.

Pro-Palestinian protesters in California

Supporters participating in a pro-Israel rally in Ventura County, California, were met by pro-Palestinian counter protesters on Sunday. (Provided to Fox News Digital)

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The Jewish Federation of Greater Los Angeles wrote that "violence against [the Jewish] people has no place in civilized society," and that they will "not tolerate violence against [the Jewish] community… [and] will do everything in [their] power to prevent it."

"Our hearts are with the family of the victim," the group wrote in a Monday night post. "While we wait for more information from our law enforcement partners, we remind you that this is the fourth major antisemitic crime committed in Los Angeles this year alone."

A man attends to Paul Kessler, who is lying on the ground bleeding

The Jewish Federation of Greater Los Angeles said the alleged attack on Kessler marks the fourth major antisemitic attack in the city this year. (Provided to Fox News Digital)

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Rep. Jerry Nadler, D-N-Y, shared the post, writing that "the explosion of antisemitism [had turned] deadly." 

"A 65-year-old(sic) Jewish man in LA was killed by a violent anti-Israel protestor(sic)," Nadler, who is Jewish, wrote. "I strongly encourage people of goodwill, people seeking peace to separate yourselves from those glorifying & committing violence. Help calm the tide of hate."

He continued: "Violent political rhetoric has consequences. After a short while it incites and dehumanizes. And like tonight, tragically, people can be hurt or killed. Our country is at a crossroads and each of us bears responsibility to help bring calm."

Former Israeli Prime Minister Benny Gantz said Kessler's "murder" is "a warning light that must reverberate throughout the world." 

"The murderous ideology of Hamas that led to the terrible massacre on Oct.7 is not only Israel's problem, and the entire free world must unite against it and fight it [to] stand on the right side of history," Gantz said, according to Israeli media.