Tom Watson dismisses Momentum as 'a bit of a rabble'
Labour's deputy leader Tom Watson has dismissed Momentum, a pressure group accused of targeting opponents of Jeremy Corbyn, as a "bit of a rabble".
The organisation - the successor group to Mr Corbyn's leadership campaign - had little impact on Labour, he said.
Mr Corbyn has been urged to distance himself from the group by MPs who say they have been victims of abuse since voting for military action in Syria.
But Ken Livingstone, a Corbyn ally, said it had a valuable role to play.
Momentum was established to give a continued voice to the thousands of people who helped elect Jeremy Corbyn as Labour leader after becoming registered supporters of the party and to ensure Mr Corbyn's anti-austerity policy platform is maintained.
Critics have warned it risks becoming a "party within the party" and that some of its supporters are not members of Labour and do not share its values.
It has come under fresh scrutiny in recent days amid claims MPs who voted to bomb so-called Islamic State in Syria have been subject to online intimidation - or threats to oust them as Labour candidates.
The group has defended its right to lobby MPs but insisted it "strongly disapproves" of anyone engaging in threatening behaviour or de-selection threats.
In the run-up to the Syria vote, it helped 30,000 people send emails urging them not to back military action.
Asked about Momentum's role in the Labour movement, Mr Watson said he was not unduly concerned about its activities.
"They look like a bit of a rabble to me, but I don't think they are a problem for the Labour Party," he told Radio 4's Today programme.
"I don't think they are effective. I think they are a bit of an irrelevance in the debate."
Momentum has denied it is pushing for MPs who disagree with Mr Corbyn on Syria and other issues to be deselected in the run-up to the next election although Mr Livingstone, who is a Momentum member, has said some MPs could find themselves being ousted for undermining the leadership.
Mr Watson told the BBC that these remarks were "not particularly helpful" at a time when the party should be trying to present a more united face after the infighting and recriminations over Syria.
"As the nearest we have to a Labour elder - he is getting on a bit, Ken - he should probably know that this is the week when we should be trying to bring people back together."
Asked if Mr Livingstone, whose role as co-convenor of Labour's defence review has caused controversy, should adopt a lower profile, Mr Watson replied: "I think that would be an impossible dream. But I think he should calm down a bit."
Mr Livingstone said he had been "quite angry" about the criticism directed at Mr Corbyn but that, in the wake of Labour's victory in the Oldham West and Royton by-election, the recent "tensions" in the party should ease a little.
He hit back at claims Momentum was the new Militant - saying it had nothing in common with that "nasty" organisation, that attempted to infiltrate Labour from the hard left in the 1980s.
"What we have in Momentum is a campaigning organisation," he told Radio 4's World at One.
"There are no doubt a lot of people there who are mildly eccentric but what we need is boots on the ground, getting voters who have been kicked off the voting list back and getting onto campaigning on exorbitant rents and all that."
It comes as Labour MPs who backed military action continued to report online abuse - despite a joint call by Mr Watson and Mr Corbyn for it to cease.
Barrow-in Furness MP John Woodcock said he had "reported to police a Facebook purportedly from Barrow inciting criminal behaviour to give me a "wake up call" after Syria vote".
Another Labour MP, Neil Coyle, has been given added police security after receiving a threatening Twitter message after he voted for military action.
The message is not thought to be linked to Momentum, but the MP for Southwark and Bermondsey South nevertheless called on Mr Corbyn to distance himself from the group to protect Labour MPs and councillors.
"Jeremy Corbyn's elected representatives are coming under pressure from people who think they are operating in the leader's name and only the leader and his team can take action to distance themselves from people who are not Labour representatives."