Helsinki, Finland - President Joe Biden said on Thursday the United States will remain a reliable NATO partner no matter what happens in next year's election, as he visited new alliance member Finland and held a mini-summit with Nordic leaders.

"I absolutely guarantee it. There is no question," Biden said when asked in Helsinki by a reporter if he could offer reassurance that Washington would stick with the Western defense alliance, of which Finland became the 31st member in April.

With less than 16 months left until the next presidential poll in the US, Republican Donald Trump is leading his party's crowded field of candidates while Biden is all but certain to get the nomination of Democrats.

Memories are fresh in Europe of Trump's skepticism toward the trans-Atlantic alliance, questioning its purpose and efficacy. At one point he called it "obsolete."

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"There's overwhelming support from the American people," Biden said of NATO. "There's overwhelming support from the members of the Congress, both House and Senate, and both parties – not withstanding the fact there’s some extreme elements of one party. We will stand together."

"No one can guarantee the future, but this is the best bet anyone could make," he said alongside Finnish President Sauli Niinistö.

Biden had traveled on to Finland after the two-day NATO summit in Vilnius, Lithuania, where Russia's invasion of Ukraine dominated talks.

In Helsinki, he met with Niinistö before attending a summit with other Nordic leaders from Denmark, Norway, Sweden, and Iceland. Those talks were dominated by security policy, technology, and the climate crisis.

There were warm words all around, with Niinistö saying Biden had helped usher in a "new era in Finnish security policy."

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"I also want to thank you for the Vilnius meeting. It was very touching to feel the unity between us. It was greatly created by you," he told Biden.

NATO's external border with Russia has more than doubled as a result of Finland's accession. At its closest point, this border is only about a two-hour drive from Helsinki – but Biden, who described NATO as "stronger" than ever, did not visit during his trip.

It was the first visit by a sitting US president since Trump went five years ago for face-to-face talks with Russian President Vladimir Putin.

Biden noted that the US and Finland had shared democratic values.

"It took me about three seconds to say yes [to the country joining]," Biden said.

In his meeting with the Nordic leaders, Biden called for close cooperation to tackle the climate crisis and said "we don't have a lot of time."

"But I'm confident if we continue to work together, we can deal with it," the US president asserted.

The Nordic countries have long played a leading role in this, Biden added.

Several of the countries are regarded as international pioneers when it comes to climate protection and renewable energies.

Denmark, for example, has set itself one of the most ambitious climate goals by 2030, aiming to reduce its emissions by 70% compared to 1990.

Iceland's Prime Minister Katrín Jakobsdóttir stressed that the US played a crucial role in tackling the climate and biodiversity crisis.

Danish Prime Minister Mette Frederiksen, meanwhile, praised Biden for bringing the US back into the fight against climate change. However, one must not only solve the climate crisis, but also create jobs and a better future for the people.

"And with you in the White House, we have an opportunity to do this together," Frederiksen said.