Sir Keir Starmer will investigate briefings that unleashed a leadership row as he faces pressure to overhaul his “toxic” Downing Street operation.
The Prime Minister apologised to Health Secretary Wes Streeting for anonymous attacks from No 10 that he was plotting a coup.
Mr Streeting said the “self-defeating” claims – which he denied – showed problems with the culture in Sir Keir’s administration.
The future of Morgan McSweeney, Sir Keir’s long-time ally and chief of staff, at the top of government is under threat, as fingers are pointed for the fallout from the apparent ploy to warn off potential leadership contenders.
Sir Keir was forced to condemn “completely unacceptable” attacks on Cabinet ministers, as he told the Commons on Wednesday: “Morgan McSweeney, my team and I are absolutely focused on delivering for the country.”
He later moved to smooth relations with Mr Streeting directly in a brief chat on Wednesday evening, their first since the hostilities erupted.
Sir Keir apologised to him for the briefing campaign, without going into details, according to a source.
The pair did not discuss Mr McSweeney and agreed to speak again soon.
Sir Keir is “looking into” the source of the attacks, Labour Party chairwoman Anna Turley said.
She told ITV: “He is going to investigate and we’ll see what happens as a consequence of that.
“But the reality is, he’s absolutely clear, this is not in his name. This is not what he wants to see and he’s determined to drive it out.”
The Labour chair added: “He was not aware of this briefing… He’s going to take action in this to make sure it doesn’t happen again.”
Asked about calls for Mr McSweeney to be sacked, Ms Turley dismissed claims he was behind the briefings as “tittle tattle” as she stressed “we don’t know who’s responsible”.
But Sir Keir is under growing pressure from within the party to dismiss his powerful aide.
Mr Streeting hit out at the “toxic culture” around the No 10 operation and called for anyone behind the “juvenile” briefing against him to be sacked.
He told Sky News: “It’s totally self-defeating briefing, not least because it’s not true, and I don’t understand how anyone thinks it’s helpful to the Prime Minister either.”
Senior No 10 sources said Sir Keir would fight any leadership challenge but suggested the briefing against the Health Secretary had not come from Downing Street.
Sir Keir told MPs that “any attack on any member of my Cabinet is completely unacceptable” and Mr Streeting was doing a “great job”.
The unrest at the top of the party comes as Labour’s poll ratings have plummeted since Sir Keir delivered a landslide general election victory in July 2024.
And it precedes Rachel Reeves’ Budget in a fortnight, which could see the party rip up its manifesto promise not to increase income tax and MPs fear a bloodbath in elections next May in English councils and the Scottish and Welsh Parliaments.
