Ed Miliband has said he is "deeply disturbed" by reports of anti-Semitism within the Oxford University Labour Club - postponing a talk until an investigation has been carried out.
The club, which counts a number of esteemed politicians as former members, including Michael Foot and David Miliband, has been rocked by claims of racism - seeing one MP call for Jeremy Corbyn to "personally look into" the claims.
Alex Chalmers, an undergraduate at Oriel College, resigned as co-chairman of the club earlier this week after claiming a large proportion of members "have some kind of problem with Jews" and some sympathise with Islamic militant group Hamas.
Reports of slurs and songs sung that amount to anti-Semitism have also been reported by the university's Jewish Society, known as JSoc.
The Doncaster North MP had been due to address the club' s annual John Smith Memorial Dinner on March 4.
A spokesman for the former Labour leader told the Press Association: "Ed is deeply disturbed to hear of reports of anti-Semitism in the Oxford University Labour Club.
"It is right that the executive of the club has roundly condemned the comments and fully co-operates with the Labour Students' investigation. Ed and the Labour Club have agreed that his talk should be postponed until the investigation is resolved."
Labour MPs say they are "deeply concerned" at the allegations while the Israeli embassy said it is "appalled" by the claims which, if true, are "abhorrent".
Labour Students, the body which Oxford University Labour Club is affiliated to, has launched an immediate investigation into the matter.
John Mann, Labour MP for Bassetlaw in Nottinghamshire, told the Press Association the Labour leader should ensure a thorough investigation is carried out.
He said: "I have written to the Labour Party asking for an investigation as a matter of urgency.
"It is hugely embarrassing for the Labour Party. This is something Jeremy Corbyn should personally look into."
MP Louise Ellman, vice chairwoman of Labour Friends of Israel, said: "I am deeply disturbed by the news that Oxford University Labour Club has decided to support Israel Apartheid Week and by the revelations from Alex Chalmers about the troubling tone of the discourse in which this debate appears to have been conducted."
She said comparisons between Israel and apartheid-era South Africa "are a grotesque smear and the Labour Party should dissociate itself from them".
The Israeli embassy in London said: "The embassy of Israel is appalled by reports of anti-Semitism, intimidation of Jewish students, and support for terrorism against Israel at the Oxford Labour Club.
"We would not expect such disgraceful activity from any morally upright person - let alone students at one of the most prestigious universities in the world.
"Anti-Semitism masquerading as politics is abhorrent. It must be recognised as such and condemned by all."
Mr Chalmers said he resigned following the club's decision to endorse Israel Apartheid Week.
In a public post on his Facebook page, he said that despite the club's "avowed commitment to liberation", the attitude of certain members towards disadvantaged groups was "becoming poisonous".
His comments, alongside allegations published by the university's Jewish Society, have sparked the investigation by Labour Students, which said it is "deeply troubled" at the reports.
A Labour Party spokeswoman said the Party "condemns anti-Semitism in any form" and that they welcome the investigation.
The executive committee of the Oxford University Labour Club said it would co-operate with the investigation.
In a statement they said: "We are horrified at and whole-heartedly condemn anti-Semitic behaviour in all its forms.
"The comments detailed in JSoc's statement last night indicate a shocking pattern of hateful and racist behaviour by some club members, and it's of the highest priority that this be dealt with swiftly and lastingly.
"Labour Students is launching an investigation; we will fully co-operate with this and encourage any of our members to come forward with any information that will assist the process."