South Bend, Indiana, Mayor Pete Buttigieg took a swipe at his 2020 rival Joe Biden for creating "the appearance of a conflict" when he was vice president by pushing for anti-corruption reforms in Ukraine while his son served on the board of a Ukrainian natural gas company.

Buttigieg, who has risen through the ranks of the Democratic primary field to become a viable challenger to Biden in multiple states, said in an Associated Press interview Monday that he "would not have wanted to see that happen" if he was in Biden's situation.

But Buttigieg quickly added that "I think this is being used to divert attention from what's really at stake in the impeachment process."

"There's been no allegation, let alone finding of any kind of wrongdoing," he told the AP in Iowa.

Biden and his son Hunter have dismissed the unsubstantiated allegations of wrongdoing related to Hunter's work for the gas company, Burisma Holdings. But President Donald Trump's request that Ukraine President Volodymyr Zelenskiy "look into" the Bidens has put the former second family at the center of the impeachment controversy in Congress.

Buttigieg said in the interview that his administration would "do everything we can to prevent even the appearance of a conflict. That's very important because as we see it can create a lot of complications even when there is no wrongdoing."

The Biden campaign declined CNBC's request for comment on Buttigieg's remarks. Buttigieg's campaign did not respond to a request for additional comment.

With the first primary contests less than five weeks away, the leading candidates are increasingly launching attacks against each other, instead of targeting Trump alone.

In a debate earlier this month, Buttigieg, who has led the pack in multiple recent polls of Iowa, weathered criticism from Sens. Elizabeth Warren and Amy Klobuchar.

But Buttigieg had previously offered a full-throated defense of the Bidens by contrasting them favorably with Trump, whom he called "a walking conflict of interest."

Biden thanked Buttigieg in October for "defending me and my family against these outrageous, lying ads of the president of the United States of America."

"That's a good man," Biden said of his primary rival.

Trump and his Republican allies have accused Biden, while serving as Barack Obama's veep, of pressuring Ukraine to fire a prosecutor there in order to protect his son from scrutiny. But Biden's stance at that time aligned with official U.S. policy and was supported by many other nations who saw that prosecutor as corrupt.

Democrats have accused Trump of pressuring Zelenskiy to announce probes against the Bidens in order to damage his possible 2020 election opponent. They add that Trump and his White House had frozen hundreds of millions of dollars in military aid to Ukraine when a July 25 call with Zelenskiy took place.

Democrats in the House voted earlier this month to impeach Trump on articles of abuse of power and obstruction of Congress related to his Ukraine dealings.