Kemi Badenoch has said there was "too much nodding along in the room and arguments outside it" in the previous Tory government as the party descended into infighting ahead of the race to replace Rishi Sunak as leader.
The shadow housing secretary's comments came after she reportedly used Mr Sunak's first shadow cabinet meeting to criticise his election campaign and potential leadership rival Suella Braverman.
Ms Badenoch on Wednesday said it was a "shame" the discussions had been leaked, after The Times reported she had accused Ms Braverman of having a "very public" nervous breakdown.
Ms Braverman hit back at her critics as "liberals" having a "meltdown".
The row came just hours after shadow home secretary James Cleverly called for the party to unite as he warned against "bitter infighting".
Mr Sunak is expected to address the 1922 Committee of backbenchers later on Wednesday after an acrimonious meeting of the panel which will set out the rules and timeline of the leadership contest.
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He announced last week that he would step down as party leader once the formal arrangements for choosing a successor are in place.
Ms Badenoch, who is considered a frontrunner in the race, reiterated the criticism of Mr Sunak's administration she reportedly voiced in the first meeting of the Conservative front bench since losing power.
She wrote in a post on X: "It's a shame our discussions in Shadow Cabinet were leaked yesterday. If there is no private space to discuss our Party's challenges, we will never fully address what the electorate told us last week.
"The views of those outside these meetings matter too. Not just backbench MPs, but our party activists, members and friends who lost seats after giving everything to the campaign.
"In government, we had too much nodding along in the room and arguments outside it. That culture needs to change. We need to be honest with one another in private, and united in the direction we take afterwards."
She did not deny attacking Mr Sunak in Tuesday's gathering of the shadow cabinet, when she reportedly called his decision to leave D-Day commemorations early "disastrous" and said colleagues including Penny Mordaunt would have kept their seats if he had stayed longer in France.
If she throws her hat in the ring, Ms Badenoch could face competition from fellow right-winger Ms Braverman.
Ms Badenoch reportedly made the nervous breakdown comments after former home secretary Ms Braverman hit out at "liberal Conservatives" at an event in Washington DC and at a Popular Conservatism gathering in London.
On Wednesday, Ms Braverman tweeted: "The liberals are having a meltdown about my speech.
"Basic truths about our Party are not easy to hear.
"But I'll keep telling them on behalf of the common sense, patriotic, conservative majority."
Other possible candidates for the party leadership include Mr Cleverly; Dame Priti Patel, who served as home secretary between July 2019 and September 2022; Robert Jenrick, who previously served as immigration minister; and ex-health secretary Victoria Atkins.
Right-wingers and more moderate Tories are expected to battle it out for the top job in a contest that could shape the party for years to come.
Shadow chancellor Jeremy Hunt, a centrist figure in the party, has ruled out running.
