Jeremy Corbyn has apparently accused MPs of "navel-gazing" after an "explosive" meeting of the Parliamentary Labour Party (PLP) in which he was heckled amid a heated row over claims of a left-wing takeover plot.
The Labour leader made a fresh plea for unity and acknowledged that "spirits can run high" because Labour is a "passionate party".
His video message was posted on Twitter hours after MPs angrily hit out at the leader's suggestion they were focused on infighting rather than campaign ahead of May's local elections, sources at the meeting said.
Others felt their questions on Mr Corbyn's strategy to revive support were not being answered, as a Guardian/ICM opinion poll showed Labour 19 points behind the Tories.
Deputy leader Tom Watson was also supported by a number of Labour politicians after publicly warning the party's future was at risk from hard-left supporters of the leader who appeared to be plotting a "secret deal" with Unite union boss Len McCluskey.
One MP described as "explosive" the discussion around Mr Watson's warnings about the apparent plans of Momentum, the grassroots activists group that helped propel Mr Corbyn to the leadership, to link up with Unite.
Mr Corbyn's team was forced to deny they were behind briefings that Mr Watson was isolated at the shadow cabinet over his warnings after PLP chair John Cryer dismissed the suggestion and a number of MPs were sharply critical.
In the video message, Mr Corbyn highlighted the role of grassroots members and said the party should "do more to involve and empower them".
"Sometimes spirits in the Labour Party can run high, today has been one of those days, that's because we're a passionate party," he said.
"To win (in May's elections), we need unity, not navel-gazing.
"My plea to all Labour Party members, whether grassroots or in senior positions is, think of our people first, think of our movement first, think of the party first.
"With mass participation of our members, Labour can win for the people of Britain."
A separate source familiar with the shadow cabinet meeting earlier on Monday acknowledged that Mr Watson was "laid into" by senior figures.
But the source insisted they were "the people who you would expect" and that other shadow cabinet ministers did not speak or were more measured in their response.
At Unison's head office in central London, the deputy leader was rounded on by shadow chancellor John McDonnell, shadow foreign secretary Emily Thornberry and shadow home secretary Diane Abbott, all close allies of the leader.
But Baroness Chakrabarti, a key member of Mr Corbyn's inner circle, was said to have been "influential" in reaching an agreement on the joint statement by the leader and deputy.
The row comes after a recording emerged of Momentum founder Jon Lansman saying he expected Unite to affiliate to the group if Mr McCluskey wins his battle for re-election as its general secretary.
After the tape emerged, Mr Watson warned a tie-up between the activist group and the union could "destroy" Labour.
The deputy Labour leader told BBC Radio 4's Today programme: "I regard this as a battle for the future existence of the Labour Party. This is high stakes.
"What Jon Lansman has outlined is a plan with Len McCluskey, the leader of Unite, to take control of the Labour Party."
Later, Mr Corbyn and Mr Watson agreed to call for party unity and insisted "no one speaks for the leadership except the leadership themselves" - viewed by supporters of the deputy as a slap-down to Mr Lansman.
In the joint statement, the leader and deputy said: "The shadow cabinet agreed on the need to strengthen party unity.
"It recognised the right of groups across the spectrum of Labour's broad church to discuss their views and try to influence the party so long as they operate within the rules.
"The leadership represents the whole party and not any one strand within it.
"No one speaks for the leadership except the leadership themselves and their spokespeople."
After the PLP meeting, the source close to Mr Corbyn claimed most Labour MPs and peers agree that groups within the party are free to try to influence it as long as it is within the rules.
"That's common ground to everybody, to both Tom and Jeremy, to the whole shadow cabinet and I'm sure to the large majority of the PLP," the source said.
Labour MP Neil Coyle hit out at Mr Corbyn's comments, tweeting: "When 'navel-gazing' = 'uncomfortable Copeland Qs' & 'more member engagement' = absolutely no frontbench Brexit consultation with members..."
Ms Thornberry said Mr Watson should not have made his concerns about Momentum and Unite public, telling BBC Newsnight: "I think that it is important that internal discussions and fights within the Labour Party are done privately, we do not need to discuss them on the media.
"It seems to me that these are things that we can discuss internally."