• Sanders apologized to Biden, said he doesn't see him as "corrupt"
  • An op-ed in The Guardian by a Sanders surrogate said Biden had a "corruption problem"
  • Biden accepted the apology, said that such attacks don't belong in the primary

Sen. Bernie Sanders, I-Vt., publicly apologized to fellow Democratic presidential candidate Joe Biden for a recent Guardian op-ed by a surrogate, who claimed the former Vice President and his campaign have a “corruption problem.” Sanders said those are “absolutely not” his views.

The author of the contentious op-ed, law professor Zephyr Teachout, does not officially work for Sanders’ campaign, but she has stumped for him. Teachout wrote that Biden “has perfected the art of taking big contributions” while going on to serve the interests of the upper-class at the expense of the rest of Americans.

“I’m sorry that op-ed appeared,” Sanders told CBS News.

Biden graciously accepted Sanders’ apology via tweet, writing that “these kinds of attacks have no place in this primary.”

Sanders’ apology is particularly unusual in the increasingly heated contest to win the Democratic Party’s nomination for president. Most recently, Sanders and Biden clashed after the former’s campaign released a video appearing to show the former vice president discussing his desire to cut Social Security at various times throughout his political career.

Biden denied wanting to ever cut Social Security and accused Sanders’ campaign of releasing “doctored” footage and having “lied” about his policies. Sanders has since said that the footage is authentic.

Speaking to CBS News, Sanders said that he believes Biden is a decent person. "He is a friend of mine. People like him. And we're not going to make personal attacks on Joe Biden but I think the record shows that Joe's history in the Senate and my history in Congress are very different.”

Sanders, whose campaigns are typically cordial toward his opponents, has been coming to blows with other Democratic nominee hopefuls as of late. Before this recent flare-up with Biden, Sanders and Sen. Elizabeth Warren, D-Mass., butted heads after it was revealed that some of Sanders’ canvassers had been given scripts that included disparaging Warren’s policies.

Despite an apology from Sanders, Warren fired back by claiming the Vermont senator had once told her a woman cannot become president. Sanders has denied the allegation.

Iowa voters will be the first to have their say in the Democratic party's nominating process with caucuses set for Feb. 3. Biden and Sanders have been battling for the top spot in the polls though most recent data shows Biden pulling out ahead.

Bernie Sanders
In this photo, Democratic presidential candidate Bernie Sanders addresses the crowd during a campaign rally at the Big Four Lawn park in Louisville, Kentucky, May 3, 2016. Getty Images/ John Sommers II