Labour needs to act more swiftly in expelling its anti-Semitic members, the Mayor of London has said.
Sadiq Khan said it is "unacceptable that people who have said things that are clearly anti-Semitic" remain within the party.
It comes as the Jewish Labour Movement (JLM) said it has no confidence in Jeremy Corbyn's leadership.
The Labour leadership have allowed a culture of antisemitism, obfuscation and denial to take hold of the Party. Our National Secretary @_petermason sets out why @tom_watson is right to get involved pic.twitter.com/i1hiz32vMH
— Jewish Labour Movement (@JewishLabour) March 2, 2019
The no confidence vote was passed "overwhelmingly" at JLM's annual general meeting on Sunday, with the group labelling Mr Corbyn "unfit" to be prime minister.
Speaking at an event marking the introduction of the Ultra Low Emission Zone in central London on Monday, Mr Khan told the Press Association: "It is unacceptable that it has taken so long to kick out racists."
He said: "I think the Labour Party has been too slow to act in relation to very serious allegations made against members of the Labour Party which are clearly anti-Semitic.
"It is unacceptable that people who have said things that are clearly anti-Semitic are still members of the Labour Party.
"I think the Labour Party needs to act more swiftly to kick out those members of our party who are racist, and if you're an anti-Semite you're a racist."
Labour has insisted Mr Corbyn was "fully committed to the support, defence and celebration of the Jewish community".
At the JLM meeting, a motion noting the "crisis of anti-Semitism" within the party since Mr Corbyn's election as leader was passed "almost unanimously".
The no confidence motion was passed despite a plea from shadow attorney general Baroness Chakrabarti not to "personalise" the issue by focusing on Mr Corbyn because he "won't be leader forever".
"My plea to the Jewish Labour Movement is to stay in the Labour movement and to tackle racism together, not to personalise it and make it about Jeremy Corbyn, because he is one person and he won't be leader forever," she said.
The JLM motion concludes that "the blame for both the crisis of anti-Semitism within the Labour Party and the party's failure to deal with it... ultimately rests with Jeremy Corbyn".
It added that "Jeremy Corbyn is therefore unfit to be prime minister" and "a Labour government led by him would not be in the interest of British Jews".
A Labour spokesman said: "Jeremy Corbyn and the Labour Party are fully committed to the support, defence and celebration of the Jewish community and its organisations.
"Anti-Semitism complaints received since April 2018 relate to about 0.1% of our membership, but one anti-Semite in our party is one too many. We are determined to tackle anti-Semitism and root it out of our Party."