Senior Labour and trade union figures have denied Labour has a problem with anti-Semitism and accused Labour MPs of whipping up the issue as part of efforts to oust Jeremy Corbyn as leader.
Shadow cabinet minister Diane Abbott said the party was the victim of a "smear" and Unite general secretary Len McCluskey dismissed the controversy as "mood music" being exploited by political enemies.
Mr Corbyn announced an independent review and pledged to tighten party codes of conduct in a bid to put a lid on the row – which has seen MP Naz Shah and close ally Ken Livingstone suspended over alleged anti-Semitic comments.
But he faced calls from Israeli politicians and diplomats to give a more "unequivocal" condemnation and warnings – including from the party's London mayoral candidate Sadiq Khan – that the party would be punished in the May 5th elections.
Sunday newspapers were full of speculation that MPs were coming closer to launching a challenge to his leadership – with a poor showing at the ballot box or a vote in favour of Brexit potentially sparking an internal coup.
Opponents have accused him of acting too slowly to deal with incidents – most notably Mr Livingstone's incendiary assertion, while defending Ms Shah, that Hitler was a Zionist before he "went mad and ended up killing six million Jews".
But allies launched a ferocious fightback and warned critics they had no chance of ousting the leader.
“It is a smear to say that the Labour Party has a problem with anti-Semitism. It is not fair on ordinary Labour Party members,” Ms Abbott – the shadow international development secretary – told BBC1’s Andrew Marr Show.
“Two hundred thousand people have joined the Labour Party. Are you saying that because there have been 12 reported incidents of hate speech online, that the Labour Party is somehow intrinsically anti-Semitic?”
Mr Livingstone’s comments – for which he has declined to apologise in a string of media interviews – were “extremely offensive” but he had been suspended within 48 hours like all those accused, she said.
She said she would be “dismayed if some people were hurling around accusations of anti-Semitism as part of some intra-Labour Party dispute” and issued a warning to plotters.
“If people are intent on having a leadership election then we may have one,” she said.
“But I have to say that if Jeremy is on the ballot then Jeremy wins. All the polling shows that he is as popular with Labour Party members now as he was when he was first elected.”
An angry Mr McCluskey – whose union is the party’s biggest donor – said Mr Corbyn was the victim of “a cynical attempt to manipulate anti-Semitism for political aims”.
“The idea that there is an anti-Semitic crisis within the Labour Party is absolutely offensive but it is being used in order to challenge Jeremy Corbyn,” he told Pienaar’s Politics on BBC Radio 5 Live.
“Once the mood music of anti-Semitism dies down, then next week and the week after there will be another subject. It is an issue that comes up because somebody says something stupid and then immediately it becomes a crisis.”
The row had been “got up by the right-wing press aided and abetted by Labour MPs” and party grandees who “get out of their wheelchair and toss a few hand grenades in”, he said.
He said MPs would be “stupid” to move against Mr Corbyn as he was “mobbed like a film star” by party members wherever he went, he suggested.
“Everybody needs to calm down, get behind the leader, and deal with issues, whether it is anti-Semitism or anything else that come up, in an appropriate manner without jumping to the tune of people who are our enemies.”
Mr Khan indicated that his prospects of being elected London mayor had been damaged by the row over Mr Livingstone – who was in charge at city hall for eight years from 2000.
The ex-minister – seen as the opposition's best hope of a positive result in elections across the United Kingdom – said the leadership had acted too slowly to tackle concerns about racist views in the ranks.
Mr Khan said: “I accept that the comments that Ken Livingstone has made make it more difficult for Londoners of Jewish faith to feel that the Labour Party is a place for them, and so I will carry on doing what I have always been doing, which is to speak for everyone.
“There are too many examples in our party of people having these views, and action does not appear to have been taken quickly enough,” he said – as he sought to fight off Tory attempts to tie him closely to Mr Livingstone and Mr Corbyn.
A poll carried out as the controversy unfolded gave the Conservatives an eight-point lead, and experts tip Labour to lose up to 150 council seats in England and face a hard night in elections to the Scottish and Welsh governments.
It came as Israel's new ambassador to Britain said parts of the left were "in denial" about anti-Semitism and criticised Mr Corbyn's links to groups such as Hizbullah and Hamas.
Mark Regev told the Andrew Marr Show that Mr Livingstone's assertion was "a horrendous perversion of history" that appeared to paint those who helped get Jews out of Nazi Germany as collaborators.
In a message to Mr Corbyn, he said: “You have had too many people on the progressive side of politics who have embraced Hamas and Hizbullah. Both of them are anti-Semitic organisations.
“Yet some progressive politicians have embraced Hamas,” he said — in an apparent reference to Mr Corbyn describing both groups as “friends” in the past.
“If you are progressive and you are embracing an organisation which is homophobic, which is misogynistic, which is openly anti-Semitic, what is progressive about that?
“There has to be an unequivocal message from leadership saying that there is no solidarity with anti-Semites.”
The leader of the Labour opposition party in Tel Aviv said recent events needed to act as a “red alert” that urgent action was required.
In an open letter to his UK counterpart, Israel's Labour leader Isaac Herzog said he had been "appalled and outraged by the recent examples of anti-Semitism by senior Labour Party officials in the United Kingdom".
“Knowing that the British Labour Party has a proud and distinguished history of fighting racism in every form, has only added to my profound disappointment at recent events, which must act as a red alert and prompt immediate action,” he wrote.
Inviting Mr Corbyn to lead a delegation to the Yad Vashem Holocaust memorial, he said that while Mr Livingstone appeared “beyond redemption” he was “sure there remain many Labour Party activists with a willingness to engage and better understand the scourge of anti-Semitism”.