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Sen. Elizabeth Warren, D-Mass., on Monday said that Sen. Bernie Sanders, I-Vt, in 2018 told her that he didn't think a woman could win the 2020 election — a statement the Sanders campaign had blasted as "a lie" earlier in the day.

"Bernie and I met for more than two hours in December 2018 to discuss the 2020 election, our past work together and our shared goals," Warren said in a statement. "Among the topics that came up was what would happen if Democrats nominated a female candidate. I thought a woman could win; he disagreed."

The statement confirmed a CNN report earlier in the day on the 2018 meeting, which Sanders and his campaign strongly denied.

"It is ludicrous to believe that at the same meeting where Elizabeth Warren told me she was going to run for president, I would tell her that a woman couldn't win. It's sad that, three weeks before the Iowa caucus and a year after that private conversation, staff who weren't in the room are lying about what happened," he said.

He added that "of course" a woman could win. "After all, Hillary Clinton beat Donald Trump by 3 million votes in 2016," Sanders said.

In her statement, Warren said "I have no interest in discussing this private meeting any further because Bernie and I have far more in common than on our differences on punditry. "We have been friends and allies in this fight for long time, and I have no doubt we will continue to work together to defeat Donald Trump and put our government on the side of the people."

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Sanders campaign manager Faiz Shakir had urged Warren to speak out on the CNN report earlier in the day, telling NBC News, "I believe strongly what we are talking about here is a lie."

"I believe that she should come out and say yeah, that is not my recollection of events, of course Bernie Sanders does not believe that," Shakir said.

The bitter back and forth between the two longtime friends comes one day before the two are due to share the stage at a Democratic presidential debate in Des Moines, Iowa.

The pair had defended each other against their more moderate rivals in past Democratic debates, but cracks in their relationship began to show in recent days after Sanders started surging in the polls.

"The timing of this clearly shows that this is a desperate move," one senior Sanders aide told NBC News. "Unfortunately Elizabeth Warren's campaign has been going down in the polls, and this is the latest in an attack on one of her leading competitors."

Politico reported over the weekend that the Sanders' campaign had been giving volunteers talking points describing Warren as the candidate of elites.

Warren said Sunday she was "disappointed" by the campaign's actions.

"I was disappointed to hear that Bernie is sending his volunteers out to trash me," she told NBC News.

Sanders downplayed the Politico report, saying his campaign has "hundreds of employees" and "people sometimes say things that they shouldn't."

"I have never said a negative word about Elizabeth Warren who is a friend of mine. We have differences on issues, that's what campaigning is about. But no one is going to be attacking Elizabeth," Sanders said.

Sanders has in the past been critical of some of Warren's policy positions, particularly health care.

In an October interview with ABC, Sanders said his Massachusetts counterpart "is a very, very good senator. But there are differences between Elizabeth and myself. Elizabeth, I think, as you know, has said that she is a capitalist through her bones. I’m not."

Before Sunday, Warren had largely avoided being critical of Sanders and his campaign, typically telling reporters asking about the differences between them that they're friends and she doesn't want to comment on other campaigns.