Tensions in the area ran so high that new groups calling for revenge against Palestinians began emerging on WhatsApp and on other messaging services like Telegram. The first WhatsApp groups appeared last Tuesday, Mr. Schatz said. By last Wednesday, his organization had found dozens of the groups.

People can join the groups through a link, many of which are shared within existing WhatsApp groups. Once they have joined one group, other groups are advertised to them.

The groups have since grown steadily in size, Mr. Schatz said. Some have become so big that they have branched off into local chapters that are dedicated to certain cities and towns. To evade detection by WhatsApp, organizers of the groups are urging people to vet new members, he said.

On Telegram, Israelis have formed roughly 20 channels to commit and plan violence against Palestinians, according to FakeReporter. Much of the content and messaging in those groups imitates what is in the WhatsApp channels.

On one new WhatsApp group that The Times reviewed, “The Revenge Troops,” people recently shared instructions for how to build Molotov cocktails and makeshift explosives. The group asked its 400 members to also provide addresses of Arab-owned businesses that could be targeted.

In another group with just under 100 members, people shared photos of guns, knives and other weapons as they discussed engaging in street combat in mixed Jewish-Arab cities. Another new WhatsApp group was named “The unapologetic right-wing group.”

After participating in attacks, members of the groups posted photos of their exploits and encouraged others to mimic them.

“We destroyed them, we left them in pieces,” said one person in “The Revenge Troops” WhatsApp group, alongside a photo showing smashed car windows. In a different group, a video was uploaded of black-clad Jewish youths stopping cars on an unnamed street and asking drivers if they were Jewish or Arab.

We beat “the enemy car-by-car,” said a comment posted underneath the video, using an expletive.

Over the weekend, Prime Minister Benjamin Netanyahu of Israel visited Lod, a mixed Jewish-Arab city in central Israel that has been the scene of recent clashes.

“There is no greater threat now than these riots, and it is essential to bring back law and order,” said Mr. Netanyahu.

Within some of the WhatsApp groups, Mr. Netanyahu’s calls for peace were ridiculed.

“Our government is too weak to do what is necessary, so we take it into our own hands,” wrote one person in a WhatsApp group dedicated to city of Ramle in central Israel. “Now that we have organized, they can’t stop us.”

Ben Decker contributed research.

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