CNN has released audio of a post-debate exchange between Bernie Sanders and Elizabeth Warren in which she accuses her 2020 Democratic opponent of calling her a "liar on national TV." The two were among six presidential candidates who participated in Tuesday night's debate in Iowa.

The two senators have been squabbling over their conflicting accounts of a meeting they had in December 2018. Warren claimed Monday that Sanders told her during that meeting that he didn't believe a woman could win, although she didn't provide specific details of the exchange. Sanders has repeatedly insisted he made no such comment, and he repeated his denial during Tuesday night's debate.

"I think you called me a liar on national TV," Warren could be heard saying in the video clip posted Wednesday night.

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"What?" Sanders asked.

"I think you called me a liar on national TV," she said again.

"You know, let's not do it right now. If you want to have that discussion, we'll have that discussion," Sanders said. Warren then replied, "Anytime."

Sanders then said: "You called me a liar. You told me — all right, let's not do it now."

Elizabeth Warren with Bernie Sanders alongside Tom Steyer at the Democratic primary debate at Drake University in Des Moines, Iowa, on January 14, 2020. Getty

At the time of the debate, the audio was not broadcast. Warren had approached Sanders with her arm out, but he appeared to speak with her briefly before walking away.

Tom Steyer could also be seen walking over to the two senators in an attempt to say hello to Sanders. Steyer told CBS News' Ed O'Keefe he did not hear what Warren and Sanders were discussing. "I was really just trying to say good night" to them, he said.

Neither the Warren or Sanders campaign immediately released a comment Wednesday night.

CNN asked Sanders about the meeting during the debate, in a question that presumed he had made the alleged comment.

"Senator Sanders, Senator Warren confirmed in a statement, that in 2018 you told her that you did not believe that a woman could win the election. Why did you say that?" asked moderator Abby Phillip.

"As a matter of fact, I didn't say it, and I don't want to waste a whole lot of time on this because this is what Donald Trump and maybe some of the media want," Sanders responded. "Anyone who knows me knows that it's incomprehensible that I would think that a woman could not be president of the United States."

Sanders noted that Hillary Clinton won the popular vote by three million votes in 2016.

"How could anybody in a million years not believe that a woman could not be president of the United States?" he asked, adding that if any of the other Democratic candidates on the stage won the presidential nomination, he would help them try to defeat President Trump in November.

Phillip followed up by asking Warren a similar question: "Senator Warren, what did you think when Senator Sanders told you a woman could not win the election?"

"I disagreed," Warren said. "Bernie is my friend, and I am not here to try and fight with Bernie."

Warren and Sanders have largely refrained from attacking one another throughout the course of the primary campaign. But that changed on the eve of Tuesday's presidential debate when the disputed meeting burst into public view.

In a statement Monday, Sanders said it was "ludicrous" to believe he would tell Warren a woman couldn't win the election. But Warren fired back with her own statement claiming that, during a two-hour meeting in December 2018, Sanders "disagreed" with her assertion that a woman could win.

On the debate stage Tuesday, Warren said that the only two candidates who could say they've won every election they've run in were herself and Senator Amy Klobuchar, the only other woman on the stage.

"This question about whether or not a woman can be president has been raised and it's time for us to attack it head on. And I think the best way to talk about who can win is by looking at people's winning records," Warren said.

"So, can a woman beat Donald Trump? Look at the men on this stage. Collectively, they have lost 10 elections. The only people on this stage who have won every single election that they've been in are the women, Amy [Klobuchar] and me."