Labour shadow international development secretary Diane Abbott has defended Jeremy Corbyn's handling of claims of anti-Semitism within the party.
Ms Abbott, a long time ally of the Labour leader, said allegations of an anti-Semitism problem in Labour were a "smear" against ordinary party members.
Unite leader Len McCluskey said the row was a "cynical attempt" to manipulate anti-Semitism for political means.
It comes after Ken Livingstone stood by his comments about Hitler and Zionism.
The former London mayor was suspended from the party after saying Adolf Hitler had supported Zionism in the 1930s "before he went mad and ended up killing six million Jews".
Speaking on the BBC's Andrew Marr Show, Ms Abbott said Mr Livingstone's remarks had been "extremely offensive", but defended the party's handling of the row.
She said there had been 12 reported cases of alleged anti-Semitism within the party since Jeremy Corbyn became leader and each had led to a suspension - including Mr Livingstone who was suspended "within hours".
"It's something of a smear against ordinary party members to say the party has a problem with anti-Semitism," she said, adding that many had spent "a lifetime fighting racism".
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Image copyright PAShe said she would be "dismayed if some people were hurling around accusations of anti-Semitism as part of some intra-Labour Party dispute".
Mr McCluskey, general secretary of trade union Unite, dismissed the controversy as "mood music" being exploited by political enemies of Mr Corbyn.
He claimed the row was "nothing more than a cynical attempt to manipulate anti-Semitism for political means" to challenge Mr Corbyn's leadership.
And he said 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".
'Too many examples'
But Labour's candidate for Mayor of London, Sadiq Khan, warned the row engulfing his party has harmed his chances of being elected.
Mr Khan told the Observer Mr Livingstone's comments had made it "more difficult" for Jewish voters to support him in next week's election.
The new Israeli ambassador to London said elements of left-wing parties were "deluding themselves" if they presumed there was no problem with anti-Semitism.
Mark Regev said language used in the past couple of weeks had been "very concerning", and there was "a difference between legitimate criticism and hate speech".
Comments in the last few weeks had crossed from criticism of Israeli government policies to "demonising and a vilification of" the Jewish state and perpetuating racist stereotypes, he said.
Israel's Labour leader Isaac Herzog also said he had been "appalled and outraged by the recent examples of anti-Semitism by senior Labour Party officials".
Mr Livingstone's comments were "horrific and unthinkable for a British politician in the 21st century", he added.
'Telling the truth'
The anti-Semitism row within the Labour Party erupted when Bradford West MP Naz Shah was suspended on Wednesday for comments she made about Israel.
Mr Livingstone defended her in a BBC interview, saying that she was not anti-Semitic.
He went on to say: "When Hitler won his election in 1932 his policy then was that Jews should be moved to Israel."
He was later confronted outside the BBC's studios by Labour MP John Mann, who accused him in front of TV cameras of being a "Nazi apologist".
Mr Livingstone was subsequently suspended but stood by his comments, saying he was "not sorry for telling the truth".
He blamed the row on "embittered Blairite MPs" seeking to scupper Labour's chances at the ballot box and prompt a leadership challenge.
Labour has said it will hold an independent inquiry into anti-Semitism and other forms of racism in its ranks, led by Shami Chakrabarti, the former head of human rights campaign group Liberty.
Labour MP Ben Bradshaw said party members had been "furious" at how the situation had been handled, but Mr Corbyn had "finally gripped it this week with this inquiry".
He added that he was increasingly of the view that Ken Livingstone was a Conservative spy who had long been planted in the Labour party and "has now emerged to try to do as much damage as he possibly can to the Labour party".