Jeremy Corbyn has faced fresh criticism from within his party over his approach to relations with the Jewish community.
The Guido Fawkes website reported that the Labour leader attended a meeting of a radical left-wing group called Jewdas, which has criticised mainstream Jewish organisations for their protests over alleged anti-Semitism.
MP John Woodcock said Mr Corbyn's attendance at the event was "irresponsible and dangerous", while the Jewish Labour Movement (JLM) also hit out at the party leader.
In a statement last week, Jewdas accused the Jewish Board of Deputies, Jewish Leadership Council and JLM of "playing a dangerous game with people's lives".
Allegations linking Mr Corbyn to anti-Semitism were "the work of cynical manipulations by people whose express loyalty is to the Conservative Party and the right wing of the Labour Party", it said.
A spokesman for Mr Corbyn said he attended an event to mark the ritual feast of Seder on Monday with Jewish people from his constituency in a personal capacity and not in his official role as Labour leader.
"Jeremy was invited to a Passover Seder with Jewish members of his local community," said the spokesman.
"He wrote to the Board of Deputies and Jewish Leadership Council last week to ask for an urgent formal meeting to discuss tackling anti-Semitism in the Labour Party and in society."
Jon Lansman, founder of the Corbyn-supporting Momentum group, said the Labour leader had not told his own office he was going to the event.
Mr Lansman, who is Jewish, said: "It was his night off, he had nothing in his official diary, his office didn't know he was there.
"So I don't think this is as significant as it's being made out."
But Mr Lansman told BBC Radio 4's Today programme: "Well, it's certainly not helpful to Jeremy or the cause of opposing anti-Semitism in the Labour Party as it happens ... and I think the important thing is that Jeremy is seeking to meet with mainstream Jewish organisations."
Momentum has said accusations of anti-Semitism "should not and cannot be dismissed simply as right-wing smears".
Labour backbencher Mr Woodcock, a prominent critic of the party leader, said Mr Corbyn's attendance at the Seder was "deliberately baiting the mainstream Jewish community days after they pleaded with him to tackle anti-Semitism".
"And he must know that meeting them now will give his members the message that the group's extreme views are OK."
Another Labour MP, Angela Smith, said Mr Corbyn's attendance at the Jewdas Seder "reads as a blatant dismissal of the case made for tackling anti-Semitism in Labour".
JLM spokesman Ivor Caplin said: "When we called on the leader of our party to show moral leadership and take decisive action to stamp out anti-Semitism, this is not what we had in mind.
"Jewish party activists have spent the weekend knocking on doors for local candidates for council elections across the country.
"They do not deserve the indignity of our leader making this situation even worse."
Jewdas shrugged off the attack, posting a Twitter message: "Great that there's so much interest in our work tonight! Please feel free to make a donation!"
Great that there's so much interest in our work tonight! Please feel free to make a donation! https://t.co/aqHwwPBlkF— jewdⒶs // ייִדהודה (@jewdas) April 2, 2018
The group said: "We are proud to be Jews and proud of everyone who attended, whether they were Jewish or not.
"We want everyone to know - we're leaving Mitzrayim (Egypt). Change is coming. Revolution will come."
And it suggested to the "good Jews" in the Board of Deputies that Mr Corbyn attended the event because Jewdas throws the best Seders.
Comedian David Baddiel, who has been at the forefront of the debate over anti-Semitism in the Labour Party, rejected suggestions that Jewdas was "despised" by other members of the Jewish community.
"No, it isn't," he said. "They are just Jews who disagree with other Jews. Which means: Jews ... To make out that it's somehow anti-Semitic for him to spend Seder with them just because they're far left is balls."
No it isn't. They are just Jews who disagree with other Jews. Which means: Jews. https://t.co/N2D3uxdbzq— David Baddiel (@Baddiel) April 2, 2018
Writer David Schneider tweeted: "Boo! Corbyn needs to get out and meets some Jews!" (Corbyn spends Passover with some Jews at Jewdas) "Boo! Not those Jews!"
“Boo! Corbyn needs to get out and meets some Jews!”
[Corbyn spends Passover with some Jews at Jewdas]
“Boo! Not those Jews!”— David Schneider (@davidschneider) April 2, 2018
Mr Corbyn has come under sustained pressure over allegations of anti-Semitism within his party. He is facing demands to speed up the investigations into a backlog of around 70 complaints, including one against his close ally, Ken Livingstone.
He has told new general secretary Jennie Formby to make dealing with the issue a top priority, asking her to appoint an in-house lawyer to ensure that procedures are "absolutely strong and watertight" throughout the party.
The Labour leader acknowledged on Monday that concerns about prejudice against Jewish people were "genuine" and vowed that he would not tolerate anti-Semitism in the party.
‘I am not tolerating any anti-Semitism in our party.’
Jeremy Corbyn responds to the latest row over anti-Semitism in the Labour Party. pic.twitter.com/u4QEPmZK0x— Channel 4 News (@Channel4News) April 2, 2018
Speaking to Channel 4 News, he said: "There is genuine concern and we are dealing with that concern ... We are not tolerating anti-Semitism in any form in the Labour Party."
Mr Corbyn said he was not aware of allegedly anti-Semitic social media posts made by a Labour candidate for local elections in Kent, but said he was suspended as soon as they came to light.