“Going forward, I will work closely with him to meet global challenges including Covid-19 and climate change,” Moon wrote on Twitter.

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Japanese media reported that Suga had agreed with Biden to meet in person “as soon as possible”, with government sources saying the prime minister is likely to visit the US after the president-elect takes office on January 20.

Article Five of the treaty obliges both parties to “act to meet the common danger” in the event of an armed attack on either party in territory administered by Japan.

Both leaders also affirmed that their nations would coordinate closely in combating global warming, Suga said.

He has already pledged to make Japan carbon-free by 2050, while Biden has underscored his commitment to bringing the US back to the United Nations Paris climate agreement, from which Trump has withdrawn.

Like Japan, South Korea also relies on the US as a nuclear deterrent against the North, and Prime Minister Moon’s administration is pinning its hopes on a restart of the stalled negotiations – which could facilitate inter-Korean economic initiatives. The plans have been hamstrung by international sanctions imposed over Pyongyang’s nuclear and missile programmes.

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“I will do my utmost to make sure the precious achievements made together under the Trump administration will be well succeeded and further developed by the next government,” he said.

Biden said the US would “cooperate closely to resolve the issue of the North’s denuclearisation”, according to a presidential Blue House spokesperson.

Biden thanked Moon for his congratulations, expressing his desire to strengthen the US-South Korea alliance “as the linchpin of security and prosperity in the Indo-Pacific region”, a statement posted on the website of Biden’s transition team said.

“He observed that he looks forward to working closely with President Moon on other shared challenges, from North Korea to climate change,” it added.

Harry J. Kazianis, a national security expert at the Centre for the National Interest, said Biden’s administration would have “every incentive to try something revolutionary that would profoundly change the dynamics on the Korean peninsula”.

“Biden can do something right away to signal even now that he will not abandon the progress that has been made just because it was ushered in by a political rival”, he wrote to the independent Hankyoreh daily.

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“Here is where words matter, for Biden should proclaim in the coming days he wants to craft a ‘new-type of relationship with North Korea’, stating clearly he never wants to go back to the dark days of 2017 when harsh rhetoric and threats of nuclear war were traded constantly.

“In the coming months, an effort must be made to work towards an agreement whereby Washington and Seoul relieve some of the pressure, by offering sanctions relief for a meaningful first step towards denuclearisation.”

He suggested Kim Yo-jong, the influential sister of the Kim Jong-un, should be invited to Washington after Biden’s inauguration.

Additional reporting by Bloomberg, Reuters, Kyodo