Attack by PLO flag-waving assailants the latest in a string of assaults on supporters of Israel.

A pro-Israel rally came under attack Sunday night outside the Federal Building in Westwood, Los Angeles - the latest in a worrying string of similar instances in the US and Europe.

More than 2,000 supporters of Israel were demonstrating peacefully against terrorist rocket fire from the Gaza Strip, and in support of the Jewish state's measures to defend itself, when witnesses say four men in a pickup truck launched a violent assault, according to the Jewish Journal.

The attackers were waving Palestine Liberation Organization (PLO) flags and reportedly began beating pro-Israel demonstrators almost immediately after pulling over next to the rally.

It is not known if they were previously taking part in a much smaller counter-demonstration of around 200 anti-Israel activists being held across the street at the same time.

Watch - Grainy footage shows the moment of the attack:

The attackers fled when police intervened to break up the confrontation which ensued. But adding to the drama a Homeland Security officer fired at least one shot with his service weapon at the vehicle in an apparent attempt to stop the attackers from fleeing, witnesses said.

Police eventually caught up with the truck at around 9:30 p.m. local time and arrested the four men - described as Palestinians living in the Anaheim area. An LAPD officer told the Jewish Journal they will all face felony assault charges.

One of them, Hany Rafai, denied that they had been involved in any kind of violence, and even managed to speak to CBS news before being taken away by police.

The pro-Israel rally was arranged by Israel advocacy group StandWithUs and the Israel American Council, and was described by IAC board member Adam Milstein as one of LA's largest-ever pro-Israel rallies.

The violent incident is just the latest in a string of assaults on supporters of Israel by anti-Zionists in less than a week since the start of Operation Protective Edge, launched by the IDF to stop rocket fire from Hamas and other terrorist groups which have targeted Israeli civilians for more than a decade.

On Friday in Boston, anti-Israel marchers surrounded a group of pro-Israel activists holding a counter demonstration, and hurled anti-Semitic abuse at them. One member of the pro-Israel group was physically assaulted by an Arab-American woman who told her that "Jews will go to hell."

And in the most alarming incident so far, a synagogue filled with worshippers was attacked by a Muslim mob in Paris Sunday night. Police in the French capital had to escort Jews from the synagogue after pushing back rioters who smashed the building's windows with rocks and attempted to break in.

Just a few weeks earlier, a pro-Israel march in protest of the abduction and murder of three Israeli teenagers came under attack in Paris, as Muslim attackers launched fireworks and charged the demonstration, resulting in at least one arrest.