US President Donald Trump will reach out to Kim Jong Un again, he said in an interview aired Thursday, calling the North Korean leader with whom he previously met three times a "smart guy".

The Republican had a rare diplomatic relationship with the reclusive Kim during his previous administration from 2017 to 2021, not only meeting with him but saying the two "fell in love".

But his own Secretary of State, Marco Rubio, acknowledged at his confirmation hearing that the effort did not produce any lasting agreement to end North Korea's nuclear programme.

When asked during a Fox News interview if he would "reach out" to Kim again, Trump replied: "I will, yeah. He liked me."

North Korea says it is seeking nuclear weapons to counter threats from the US and its allies, including South Korea.

The two Koreas remain technically at war since the 1950 to 1953 conflict ended in an armistice not a peace treaty.

The isolated and impoverished North, which has conducted multiple nuclear tests and periodically test fires missiles from its ballistic arsenal, also likes to tout its nuclear programme as a sign of its prestige.

Washington and others warn that the programme is destabilising, however, and the UN has passed multiple resolutions banning North Korea's efforts.

Rubio branded Kim a "dictator" during his Senate confirmation hearing earlier this month.

"I think there has to be an appetite for a very serious look at broader North Korean policies," Rubio said.

Rubio called for efforts to prevent a war by North Korea with South Korea and Japan and to see "what can we do to prevent a crisis without encouraging other nation-states to pursue their own nuclear weapons programmes:.

During the Fox interview, Trump recalled his attempt to reach an arms deal with North Korea's allies Russia and China at the end of his first term.

The 2019 effort would have set new limits for unregulated Russian nuclear weapons and to persuade China to join an arms control pact, according to reports from the time.

"I was very close to having a deal. I would have made a deal with (Russian leader Vladimir) Putin on that, denuclearisation ... But we had a bad election that interrupted us," he said, referring to his 2020 loss to Democrat Joe Biden.

Trump's nominee to lead the Pentagon, Pete Hegseth, recently labelled North Korea as a "nuclear power" in a statement submitted to a Senate panel, according to reports.

Seoul's defence ministry said in response that Pyongyang's status as a nuclear power "cannot be recognised" and that it will work with Washington to denuclearise.

Pyongyang fired several short-range ballistic missiles in the days leading up to Trump's inauguration on January 20, prompting analysts to speculate on whether Kim was seeking to send a message to Trump.

AFP