British police arrested four people over videos shared on social media in which anti-Semitic and misogynist language can be heard being shouted during a pro-Palestinian protest.
The footage shows a convoy of cars adorned with Palestinian flags driving through a part of north London with a large Jewish population.
At one point a man’s voice can be heard through a loudspeaker shouting profanities and saying: “Rape their daughters.”
Sadiq Khan, the mayor of the UK capital, said extra officers would be on hand to “reassure Londoners, particularly those from Jewish communities”, who were worried about hate crime.
“Unfortunately, we’ve seen it in recent years, whenever there is tension in the Middle East and violence, it can spill over into our city,” Mr Khan told ITV.
“Our city is the most diverse city in the world.”
Mr Khan also tweeted: “Hate crimes are inexcusable and have no place in our city. I’ve been in touch with the Met Police Commissioner about the appalling reports of anti-Semitism attacks this weekend.”
Communities Secretary Robert Jenrick described events over the weekend as "intimidatory, racist and extremely serious crimes".
"Every time the virus of anti-Semitism re-enters our society it masks itself as social justice," he said.
Tell Mama, a group that records anti-Muslim hate incidents, said the video was “causing significant fear, alarm and distress within Jewish communities”.
“We know that people’s emotions are heightened at this time. But this does not give anyone the right to spread anti-Semitism, or anti-Muslim hate,” Tell Mama said.
The Palestine Solidarity Campaign, which helped organised a protest in support of Palestinians on Saturday, condemned the incident.
“The vile anti-Semitism shouted today from a convoy of cars has no place in the Palestine solidarity movement,” it said.
“We condemn it and all anti-Semitism, on its own account and also as it serves to undermine the anti-racist struggle for Palestinian rights.”
The Metropolitan Police said officers stopped a car on a main road in west London and detained four men on suspicion of racially aggravated public order offences.
“This behaviour was utterly shocking and will not be tolerated,” Supt Jo Edwards said.
Prime Minister Boris Johnson also condemned the footage, which came just before the Jewish festival of Shavuot started.
“There is no place for anti-Semitism in our society,” he said on Twitter.
“Ahead of Shavuot, I stand with Britain’s Jews who should not have to endure the type of shameful racism we have seen today.”
Keir Starmer, leader of the opposition Labour Party, decried the incident, saying it was “utterly disgusting”.
“Anti-Semitism, misogyny and hate have no place on our streets or in our society,” he said. “There must be consequences.”
On Saturday, thousands of demonstrators gathered outside the Israeli embassy in London to protest against Israel's strikes on Gaza during a week of conflict that included Gazan militias firing rockets into Israel.
It was one of scores of protests around the world.
At least 192 Palestinians and 10 Israelis have been killed in the worst Israeli-Palestinian violence since the 50-day war in Gaza in 2014.