Shadow Chancellor John McDonnell has said he "does not recognise" the claim that Jeremy Corbyn's team wanted a "faction fight" in the Labour Party.
It comes after leadership hopeful Lisa Nandy said that some of Mr Corbyn's team wanted to wage a "factional war until the other side had been crushed".
Mr McDonnell said he disagreed, but added that there had always been "a bit of a tussle" between left and right.
Rebecca Long-Bailey and Keir Starmer are also running for leadership.
Speaking to the BBC's Laura Kuenssberg on Friday, Ms Nandy said she raised her concerns about "faction fighting" with the Labour leader before she quit his shadow cabinet in 2016.
The Wigan MP joined a mass walkout of so-called "moderate" shadow ministers in 2016, triggered by Labour's poor European election performance and Mr Corbyn's decision to sack Hilary Benn.
She insisted that she had tried, with a group of "soft left" MPs, to hold the team together at a meeting with Mr Corbyn and other senior figures.
But the attitude of those around Mr Corbyn made her decide to quit as shadow energy secretary, she told the BBC's political editor.
"Some senior politicians in his own team, they made it very, very clear that they were going to continue to wage that factional war until the other side had been crushed," she said.
She said it was "one thing" to have backbenchers waging factional wars with colleagues but "quite another thing to hear the leadership of the Labour Party state a commitment to doing that".
She added: "It wasn't Jeremy but there was no point at all at which he contradicted that."
'Look to future'
Asked about the comments on the BBC's Andrew Marr programme, Mr McDonnell said: "We want to unite the party - I'm sorry I just don't recognise any of that, let's just move on.
"All of the three candidates have said they want to unite the party and look to the future, let's do that."
The shadow chancellor, who is backing Mrs Long-Bailey for leader and Richard Burgon for deputy leader in the party's leadership contest, said the party was "doing our best" in providing an effective opposition.
But he agreed that "if there's a lesson for the future, let's have shorter leadership elections... it's a bit interminable, I accept that".
Asked about predictions that Labour faces disastrous local election results in May, Mr McDonnell said he is "confident".
The leadership contest ballot closes on 2 April, with the new Labour leader announced on 4 April.