INDIANOLA, Iowa — Former Vice President Joe Biden demanded an apology Saturday from Bernie Sanders' presidential campaign for circulating what he called a "doctored" video misconstruing his record on Social Security.

Biden, a Democratic rival for the nomination, responded to a question from a woman who told him that she received a call from a campaign questioning Biden's position on Social Security and Medicare. He told the audience that "Bernie's people" had circulated a video that falsely suggested that he agreed in 2018 with the position of Paul Ryan, the House speaker at the time, to dismantle the benefits.

"But it is simply a lie, that video that is going around, and ask anybody in the press, it's a flat lie. They've acknowledged that this is a doctored tape," Biden said before pointing to a PolitiFact article outlining falsehoods from the Sanders campaign. "And I think it's beneath him, and I'm looking for his campaign to come forward and disown it, but they haven't done it yet."

The video was posted by an unverified Twitter user and retweeted this month by a senior Sanders campaign adviser. The video clipped remarks Biden made at the Brookings Institution in April 2018, showing Biden saying Ryan was "correct" in trying to dismantle Social Security, a remark his campaign says he made sarcastically.

"The Sanders campaign has pushed a video and transcript that were intentionally, deceptively edited to make it seem like Vice President Biden was praising and agreeing with Paul Ryan, when it is clear he was doing the exact opposite," a Biden campaign official said in a statement. "In the speech, Biden was reiterating his core belief that we need to undo Trump's tax cuts for the super wealthy and replace them with a tax code that rewards work, not just wealth."

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Sanders campaign officials have also posted videos, mainly from Biden's time in the Senate, in which Biden discusses contemporaneous proposals that would have affected Social Security benefits. They have sought to contrast Biden's history with Sanders' and to cast Sanders, I-Vt., as an unflinching defender of the program.

In response to Biden's demand for an apology, Sanders pushed back in a statement and told Biden to stop "dodging questions about his record."

"Joe Biden should be honest with voters and stop trying to doctor his own public record of consistently and repeatedly trying to cut Social Security. The facts are very clear: Biden not only pushed to cut Social Security — he is on tape proudly bragging about it on multiple occasions," Sanders said.

His campaign also immediately blasted out a memo titled "Joe Biden's Record on Social Security," listing video, statements and quotations of Biden talking about the program as far back as 1984.

Biden's response came after numerous Sanders campaign advisers and the candidate himself had launched attacks against the former vice president's record on Social Security.

In recent weeks, Sanders has continued to call attention to Biden's Iraq War vote and long political record — which he described as "baggage"— to dismantle Biden's argument that he's ready to be this era's Democratic leader.

Moments before the Biden official's statement was released, Sanders warned a crowd in Exeter, New Hampshire, that Democratic infighting would only hurt the party's chances of defeating President Donald Trump.

"I think the best thing for all Democratic candidates, and what we're going to do in our campaign, as you heard me tonight, you didn't hear me say a word about any of the other candidates," he said. "We are going to focus on the issues of the working families of America and bring them together."

CORRECTION (Jan. 19, 2020, 10:35 a.m. ET): An earlier version of this article mistakenly attributed a quotation. The following quotation was said by Bernie Sanders, not Joe Biden: "I think the best thing for all Democratic candidates, and what we're going to do in our campaign, as you heard me tonight, you didn't hear me say a word about any of the other candidates. We are going to focus on the issues of the working families of America and bring them together."