MARSHALLTOWN, Iowa — Sen. Elizabeth Warren, D-Mass., on Sunday called on Sen. Bernie Sanders, her fellow 2020 Democratic presidential contender, to turn his campaign "in a different direction" after it reportedly provided talking points to its volunteers instructing them to paint Warren as the candidate of elites in conversations with voters.

"I was disappointed to hear that Bernie is sending his volunteers out to trash me," she told NBC News. "Bernie knows me and has known me for a long time. He knows who I am, where I come from, what I have worked on and fought for and the coalition and grassroots movement we are trying to build. Democrats want to win in 2020 we all saw the impact of the factionalism in 2016 and we can't have a repeat of that."

Warren added that Democrats "need to unite our party."

"We cannot nominate someone who takes big chunks of the Democratic Coalition for granted," she added. "We need someone who will bring our party together. We need someone who will excite every part of the Democratic Party, someone who will be there. Someone that every Democrat can believe in. I hope Bernie reconsiders and turns his campaign in a different direction."

Warren's comments followed a Politico report which said Sanders' campaign is providing talking points to volunteers that say Warren is the candidate of elites who will not expand the Democratic base. The script, obtained by Politico, instructs volunteers to say Warren's supporters "are highly-educated, more affluent people who are going to show up and vote Democratic no matter what” and that “she's bringing no new bases into the Democratic Party.”

The Sanders campaign declined to comment to Politico but did not challenge the authenticity of the document.

Sanders responded to Warren's comments later Sunday, telling reporters in Iowa City that the kerfuffle amounted to "a little bit of a media blow up that kinda wants conflict."

"Elizabeth Warren is a very good friend of mine, we have worked together in the Senate for years, Elizabeth Warren and I will continue to work together, we will debate the issues, no one is gonna trash Elizabeth Warren," he said, adding that his campaign has "hundreds of employees" and "people sometimes say things that they shouldn't."

Sanders pointed to his past remarks, saying he's never said a bad word about Warren.

"We have over 500 people on our campaign. People do certain things, I'm sure that in Elizabeth's campaign, people do certain things as well," Sanders added. "But you heard me for months, 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 gonna be attacking Elizabeth."

Sen. Elizabeth Warren, D-Mass., speaks at a campaign event in Iowa on Sunday. Patrick Semansky / AP

Warren's remarks on Sunday appeared to be her most direct shot yet at Sanders and his campaign. In the past, she’s declined to draw any differences between her and Sanders, when asked by reporters and even when asked by voters. She’ll often say she and Sanders are friends and that she’s not here to comment on other campaigns. Sanders has also generally shied away from direct attacks, though he has made some critical remarks about her policies.

Sanders, I-Vt., has jumped into first place in both Iowa and New Hampshire, according to the RealClearPolitics polling average. He and his campaign have increasingly taken aim at his top rivals, such as Warren and former Vice President Joe Biden, as the first contests approach.

President Donald Trump has taken notice of Sanders' improved standing on Sunday, tweeting, "Wow!"

"Crazy Bernie Sanders is surging in the polls, looking very good against his opponents in the Do Nothing Party," Trump wrote. "So what does this all mean? Stay tuned!"

"It means you're going to lose," Sanders fired back.