The leaders of the United States, South Korea and Japan have held a joint news conference to denounce the growing military cooperation between North Korea and Russia.

Held on the sidelines of the Asia-Pacific Economic Cooperation (APEC) summit in Lima, Peru, the conference also served as a swan song for outgoing US President Joe Biden, who will be leaving office in 2025.

“We’ve now reached a moment of significant political change,” Biden told reporters on Friday. He touted the bonds between the US, South Korea and Japan as a major part of his legacy.

“This is likely to be my last trilateral meeting with this important group, but I’m proud to have helped be one of the parts of building this partnership, and I think it’s built to last. That’s my hope and expectation.”

Biden will be replaced in January by incoming President-elect Donald Trump, a Republican who champions an “America First” foreign policy.

Those shifting political tailwinds may be critical as Japan, South Korea and the US cooperate in their efforts to contain the nuclear threat they perceive in North Korea, also known as the Democratic People’s Republic of Korea (DPRK).

Earlier this week, North Korea signed into law a military treaty with another nuclear power, Russia, to bolster the latter’s war in Ukraine.

The agreement includes a mutual defence pact, and already, up to 10,000 North Korean troops have reportedly been sent to Russia’s border with Ukraine.

Biden emphasised on Friday that the US alliance with Japan and South Korea would be pivotal to “countering North Korea’s dangerous and destabilizing cooperation with Russia”.

South Korea’s President Yoon Suk-yeol echoed that sentiment, citing the increasing presence of North Korean troops abroad.

“As we can see from the recent deployment of DPRK troops to Russia, the challenging security environment within and outside the region once again reminds us of the importance of our trilateral cooperation,” Yoon said.

He and Biden were also joined by Japanese Prime Minister Ishiba Shigeru, who took office in October.

Shigeru has been vocal in pushing for a more balanced relationship between his country and the US, including proposing shared management of American military bases in Japan.

Top leaders from the three countries met for the first time in a standalone format last year, in August 2023.

On Friday, Yoon expressed a hope that the leaders could continue to meet every year, in order to shore up their relations.

The leaders’ news conference coincided with a firmly worded joint statement, in which the three countries reiterated their commitment to Ukraine’s “inherent right to self-defence”.

“Japan, the ROK [South Korea] and the United States strongly condemn the decisions by the leaders of the DPRK and Russia to dangerously expand Russia’s war of aggression against Ukraine,” the statement reads.

“Deepening military cooperation between the DPRK and Russia, including munitions and ballistic missile transfers, is particularly egregious given Russia’s status as a Permanent Member of the UN Security Council.”

But Trump’s impending return to the White House for a second term has raised questions about the US’s continued commitment to Ukraine’s defence.

There has been growing resistance to continued military aid to Ukraine in the US Congress, particularly among Republicans.

Last year, for instance, Republican Senator Josh Hawley called for pulling US funds altogether: “Any funding for Ukraine should be redirected to Israel immediately.”

Trump himself campaigned on a platform of bringing peace to world conflicts and ending much of the US engagement abroad. Critics speculate that his “America First” policy may be a recipe for greater isolationism.

There has also been scrutiny over the compromises Trump’s peace plans may entail.

After the Republican’s victory in the November 5 presidential election, a former adviser to the president-elect indicated to BBC News that Trump would be willing to sacrifice Ukrainian territory in the name of ending the conflict.

“If [Ukrainian] President [Volodymyr] Zelenskyy comes to the table and says, ‘Well, we can only have peace if we have Crimea,’ he shows to us that he’s not serious,” the former adviser, Bryan Lanza, said. “Crimea is gone.”

The Trump transition team has since distanced itself from Lanza’s comments, telling the BBC that Lanza “does not speak” for the president-elect.

US media reports have indicated that Biden, in his final days in office, plans to rush aid to Ukraine, in order to ensure its continued ability to defend itself from Russian invasion.