Democratic candidate Joe Biden on Thursday denounced President Donald Trump for befriending North Korea's "thug" leader, likening his diplomacy to working with Hitler.
In a sharp clash in their final presidential debate, Biden attacked Trump's insistence that he has avoided war through his summits with Kim Jong Un.
"He's talked about his good buddy, who's a thug," Biden said of the young North Korean leader.
"That's like saying we had a good relationship with Hitler before he invaded Europe - the rest of Europe. Come on."
But Biden indicated he was also willing to meet with Kim, saying his condition would be that Pyongyang works to make the Korean peninsula "a nuclear-free zone."
Trump said that former president Barack Obama had left him "a mess" on North Korea and had warned him of the risk of "nuclear war".
After the summits, "we have a very good relationship. And there's no war," said Trump, who also played down North Korea's recent unveiling of a massive new long-range missile at a military parade.
"He didn't like Obama," Trump said of Kim not meeting the former president. "He didn't like him. He wouldn't do it."
Biden, who was vice president under Obama, hit back that Obama would not meet Kim because he was pushing stronger sanctions.
"President Obama said we're going to talk about denuclearisation. We're not going to legitimise you."
Trump first met in June 2018 with Kim in Singapore, the first-ever summit between the countries still technically at war, and later said that the two leaders "fell in love".
The two leaders have met two more times and North Korea has since held off on nuclear and missile tests but analysts say Pyongyang has kept advancing its weapons programmes.