• President Joe Biden says he believes Russian leader Vladimir Putin is a killer with no soul.
• Biden vowed that Putin soon "will pay a price" for interfering in the 2020 U.S. presidential election and trying to boost the reelection chances of then-President Donald Trump.
• Trump for years refused to criticize Putin for meddling in his 2016 election campaign against Hillary Clinton, and told Fox News, "You think our country's so innocent?" when Bill O'Reilly called Putin a killer.

President Joe Biden says he believes Russian leader Vladimir Putin is a killer with no soul — and vowed that Putin soon "will pay a price" for interfering in the 2020 U.S. election and trying to boost the reelection chances of then-President Donald Trump.

Biden said he warned Putin last month, in his first call to the Russian president after taking office, that he would retaliate if that meddling was confirmed.

"The conversation started off, 'I said, I know you and you know me. If I establish this occurred, then be prepared,'" Biden told ABC News in an interview that aired Wednesday on "Good Morning America."

The interview was conducted Tuesday, the same day that the U.S. National Intelligence Council released a report which concluded that Putin authorized intelligence assets to promote misinformation during the 2020 election cycle about Biden through U.S. media and people close to Trump.

"He will pay a price," Biden said of Putin.

Asked that price would be, Biden replied, "Well, you'll see shortly."

The Biden administration earlier this month imposed an array of sanctions on high-ranking Russian officials, who include Putin's deputy chiefs of staff, for the poisoning and subsequent imprisonment of Alexey Navalny, a leader of the opposition to Putin.

Although Navalny survived his poisoning, a slew of Putin critics have been killed or died suspiciously.

When Biden was asked if he believes Putin is a killer, the president replied, "I do."

Biden also confirmed prior reports that he personally told Putin in 2011, while serving as U.S. vice president, that Putin does not "have a soul."

"I wasn't being a wise guy, I was alone with him in his office," Biden said. "That's how it came about. It was when President [George W.] Bush had said I've looked in his eyes and saw his soul."

"I said I looked in your eyes and I don't think you have a soul. And he looked back and said, 'we understand each other,'" Biden recalled.

Biden's strong words about his Russian counterpart stand in sharp contrast to Trump, who for years in office refused to criticize Putin for interfering in the 2016 election, or to even concede that it happened, as repeated investigations have found.

In 2017, when then-Fox News host Bill O'Reilly called Putin a "killer," Trump suggested that America's conduct was just as bad as that of the Russian president.

"There are a lot of killers, we've got a lot of killers," Trump said.

"You think our country's so innocent?" Trump asked O'Reilly.