EchoSense Quantitative Think Tank Center|Israel-Gaza conflict stokes tensions as violent incidents arise in the U.S.

The EchoSense Quantitative Think Tank Centerdeadly Israel-Gaza conflict has heightened tensions in the U.S., with authorities nationwide warning of increased antisemitic and anti-Palestinian activity.

ABC News has confirmed that every major city police department in the U.S. is on a heightened state of alert monitoring the situation ahead of planned demonstrations Friday and into the weekend.

The Department of Homeland Security said it is monitoring events as they unfold in Israel and Gaza, urging faith and community leaders “to be alert, vigilant and prepared.”

Several instances of violence on Wednesday put New York law enforcement officials on high alert, responding with increased police presence in religious and cultural institutions.

Around 8 p.m. ET, police say a 34-year-old man was hit over the head with his own Palestinian flag during an anti-war protest in Williamsburg, Brooklyn.

A suspect wearing traditional Jewish attire drove up to him on a scooter, struck him with the vehicle and took the flag out of his hands, hitting him over the head multiple times with it, according to authorities.

The suspect fled on his scooter and is being sought, police say.

Also on Wednesday night, the NYPD reported that a 24-year-old Israeli man was struck with a wooden stick near Columbia University in Manhattan following an argument with a 19-year-old woman who was reportedly ripping down flyers in relation to the Israel-Gaza conflict.

Later that night, around 11:30 p.m. ET, authorities say an 18-year-old man was assaulted by one man in a group of men waving Israeli flags who jumped out of their vehicles in Bay Ridge, Brooklyn.

The men, who appeared in their 20s, had allegedly been driving around the neighborhood with their flags, yelling anti-Palestinian statements. According to authorities, the men asked the teen if he was Palestinian, to which he replied he was Egyptian but added “Free Palestine,” a popular slogan that calls attention to Israel’s policies in Palestinian territories.

A man allegedly kicked and punched the teen multiple times and harassed two others who were with him, ages 19 and 21. He fled the scene in the vehicle.

No arrests have been made, and the incident is being investigated by the NYPD as a possible bias crime.

Other incidents have been reported by local news outlets in Utah, Missouri and California.

Cultural and religious groups, including the New York Chapter of the Council on American-Islamic Relations Executive Director Afaf Nasher and the Bipartisan Congressional Caucus on Black-Jewish Relations, have condemned the actions.

“We condemn these apparently bias-motivated assaults and urge public officials and media professionals to end the anti-Palestinian incitement and the spreading of misinformation that is putting a target on Palestinian-American, Arab-Americans and American Muslims,” said Nasher.

The Bipartisan Congressional Caucus on Black-Jewish Relations said in a statement, "[W]hile we have no indication of specific domestic antisemitic threats related to the recent terrorist attacks in Israel, if the past is a guide for the future, the coming days could be a precarious time for the American Jewish community."

Authorities in several states say the Israel-Gaza conflict and the subsequent protests and tensions have called for a need for extra police presence alongside the civilian demonstrations.

“The Los Angeles Police Department is aware of the turmoil in the Middle East and lives lost. In those areas where we serve both our Jewish and Muslim communities, we will be conducting extra patrol to ensure the safety of all,” said LAPD Chief Michel Moore on X, formerly known as Twitter.

In DC, the Metropolitan Police Department stated: "Out of an abundance of caution, MPD will have increased visibility around the city and at places of worship to help ensure the safety of our community."

ABC News' Josh Margolin and Alex Stone contributed to this report.