ReutersSir Keir Starmer has called for police to prosecute people chanting "globalise the intifada" during demonstrations, calling it an example of "extreme racism".
Speaking after two Jewish men were stabbed in Golders Green on Wednesday, the prime minister said the chant, based on an Arabic word for uprising, had left Jews feeling "scared, intimidated, wondering if they belong".
He added that the government was also looking at what "further measures we can take on protests", as it responds to concerns over rising antisemitism.
He called on people to "open their eyes to Jewish pain", adding that the issue was "about society every bit as much as it is about security".
Wednesday's attack in the north London suburb, which police have declared a terror incident, has reignited debates over the protection of British Jews and the policing of pro-Palestinian marches.
Speaking at a news conference earlier, Sir Keir said there were too many people who "don't want to see" examples of antisemitism in British society.
"Of course we protect freedom of speech and peaceful protests in this country, but if you are marching with people wearing pictures of paragliders without calling it out, you are venerating the murder of Jews," he said.
"If you stand alongside people who say globalise the intifada, you are calling for terrorism against Jews - and people who use that phrase should be prosecuted.
"It is racism, extreme racism and it has left a minority community in this country scared, intimidated, wondering if they belong."
Government review
Sir Keir's comments at the news conference mark the prime minister's strongest public comments yet about the approach he wants to see forces take to marches.
A government review of public order and hate crime legislation, commissioned after two Jewish people were killed in an attack outside a synagogue in Manchester last year, is yet to report back.
Since Wednesday's attack, however, the government's adviser on terrorism, Jonathan Hall KC, has called for a "moratorium" on pro-Palestinian marches, adding it was "clearly impossible at the moment" for them not to "incubate" antisemitism.
Both the Conservatives and Reform UK have called for the government to take a tougher approach to the demonstrations.
But Green Party leader Zack Polanski has said it would be wrong if Wednesday's "abhorrent" attack "curtails our civil liberties".
"For a government to seek to use the pain of the Jewish community to restrict our right to peaceful protest would be a dangerous error," he said.
