Jeremy Corbyn has said he is "sincerely sorry" for the pain caused by "pockets of anti-Semitism" in the Labour party.
In a statement, the Labour leader said he would be meeting representatives of the Jewish community this week to "rebuild" confidence in his party.
He said Labour was "anti-racist" and he "utterly condemns" anti-Semitism.
The comments came after Mr Corbyn was criticised for sending an apparently supportive message to the creator of an allegedly anti-Semitic mural in 2012.
In a message sent via Facebook, he had appeared to question a decision to remove the artist's controversial mural. He later called the mural "deeply disturbing" and backed its removal.
'Stamp this out'
Mr Corbyn's statement, which was released on Sunday evening, said: "I want to be clear that I will not tolerate any form of anti-Semitism that exists in and around our movement.
"We must stamp this out from our party and movement.
"We recognise that anti-Semitism has occurred in pockets within the Labour Party, causing pain and hurt to our Jewish community in the Labour Party and the rest of the country.
"I am sincerely sorry for the pain which has been caused.
Mr Corbyn said he and the party - which has "deep roots in the Jewish community" - were now campaigning to "increase support and confidence in Labour" among Jewish people in Britain.
He said: "I will be meeting representatives from the Jewish community over the coming days, weeks and months to rebuild that confidence in Labour as a party which gives effective voice to Jewish concerns and is implacably opposed to anti-Semitism in all its forms."
The statement came after Jewish community leaders organised a protest in Westminster on Monday.
The Jewish Leadership Council and the Board of Deputies of British Jews said "enough is enough", announcing they will deliver a letter to the Parliamentary Labour Party.
The Campaign Against Anti-Semitism group has also called for a national protest against anti-Semitism in Labour.
The group has compiled a list of complaints against Mr Corbyn and deputy leader Tom Watson, who on Sunday also apologised for any hurt caused.
What caused the row?
In October 2012, street artist Mear One posted a picture of his mural in east London called "Freedom of Humanity" on Facebook, with the words: "Tomorrow they want to buff my mural. Freedom of expression. London calling. Public Art."
Mr Corbyn replied: "Why? You are in good company. Rockerfeller destroyed Diego Viera's mural because it includes a picture of Lenin."
More recently, Labour MP Luciana Berger sought clarification from the leader's office on the 2012 comments.
I asked the Leader’s Office for an explanation about this Facebook post first thing this morning. I’m still waiting for a response. pic.twitter.com/DL8ynBtES4— Luciana Berger (@lucianaberger) March 23, 2018
Mr Corbyn said: "I sincerely regret that I did not look more closely at the image I was commenting on, the contents of which are deeply disturbing and anti-Semitic.
"I am opposed to the production of anti-Semitic material of any kind, and the defence of free speech cannot be used as a justification for the promotion of anti-Semitism in any form."
Mear One - whose real name is Kalen Ockerman - has denied being anti-Semitic, saying the mural was about "class and privilege".
On Sunday, senior Labour figures joined in condemnation of the mural but defended Mr Corbyn.
Shadow transport secretary Andy McDonald told Sky News that Mr Corbyn "hasn't got an anti-Semitic bone in his body" and that the row had "misinterpreted the intentions of a really good and decent man".
And Labour's Shadow Brexit Secretary Sir Keir Starmer said the mural was "grotesque and disgusting" but that Mr Corbyn had given his explanation for his online comment.
Deputy Labour leader Mr Watson told the BBC's Andrew Marr Show: "I am very, very sorry that people feel hurt by this and that is why I think it is right that Jeremy has expressed regret for it."
On Friday, Labour MP Angela Smith joined other members in supporting Ms Berger and sent a statement to the Leader's Office, calling for Mr Corbyn to appear before MPs to explain himself.
Yvette Cooper tweeted that she was "really troubled by the mural" and that "Labour must be better than this".