Joe Biden with Yoon Suk Yeol (centre left) speaks in Pyeongtaek, South Korea. AP

Biden said he was "not concerned" about new North Korean nuclear tests, which would be the first in nearly five years.

But his wry response when asked what message he had for Kim underscored the administration's low-key approach to the unresolved tensions with North Korea. It is a stark contrast with former President Donald Trump's showy threats, summits, and "love letters" with Kim.

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Neither president's approach has led to a major breakthrough, however, and North Korea has resumed testing its largest intercontinental ballistic missiles (ICBMs), while intelligence reports suggest it is preparing for a new nuclear test.

"We are prepared for anything North Korea does,” Biden said.

US President Joe Biden greets the US troops’ families in South Korea. Reuters

A day earlier, Biden and his new South Korean counterpart, President Yoon Suk-yeol, agreed to consider bigger military exercises and potentially deploying more nuclear-capable American weapons to the region in response to the North's weapons tests.

North Korea has not responded to US overtures, including offers of COVID-19 vaccines, Biden said on Saturday, noting that he was willing to sit down with Kim if he thought it would lead to a serious breakthrough.

COVID-19 restrictions may be playing a role in North Korea's lack of response, a senior US administration official said.

North Korea has said the US overtures are insincere because Washington maintains "hostile policies" such as military drills and sanctions.

When asked whether Biden was willing to take concrete steps to break the stalemate, the official said that the administration was looking for serious engagement, not grand gestures.

"This is a decision that only the DPRK can make," the official said, using the initials of North Korea's official name.

Reuters