By Max Hunder

KYIV (Reuters) - The United States will lose if Russia wins its war in Ukraine, Finland's president said on Monday, as fears mount in Europe about President Donald Trump's intentions three years after Moscow's invasion.

"The war in Ukraine is not only about Ukrainian independence, sovereignty, and territorial integrity - it is about European security, and it is about American leadership," President Alexander Stubb told Reuters in an interview in Ukraine's capital.

He spoke on the sidelines of an event attended by 11 foreign leaders to commemorate three years since Russia invaded its neighbour, as Kyiv seeks to consolidate support from its allies while its relationship with its largest backer, the U.S., hangs in the balance.

Stubb said he had no concerns about the strength of the alliance, which his country joined in 2023 after decades of balancing its foreign policy between East and West, adding that Finland was a "security provider, not a security consumer".

"We just doubled NATO's border with Russia. We have one of the largest militaries in Europe. We've always kept our defence expenditure up, and for an obvious reason, and that reason is not Stockholm, it's Moscow."

"If there's an iota or an inkling of understanding that Putin wins this peace, then the United States will have lost, so I think we need to fight this to the bitter end," he said when asked what his message to Trump would be.

EUROPE NEEDS MORE DEFENCE SPENDING

Trump, who controls NATO's most powerful military force, has questioned existing U.S. military commitments to the alliance, accusing Europe of not spending its fair share on defence.  

"There is definitely a shift in the transatlantic alliance ... the United States, I think correctly, is putting some demands on Europe of taking more responsibility for its own security." 

"It's time for the Europeans to step up to the plate and have some skin in the game, so there's definitely a shift. I am not worried," he said.

In the interview, Stubb put forward a broad vision for a peace plan in Ukraine in several phases.

The first would be a pre-negotiation strengthening of Ukraine's hand and pressuring of Russia, the second would be a ceasefire with security guarantees for Ukraine supported by Europe and backstopped by the U.S., and the third would be a peace process which discusses issues such as territory, finances and reconstruction.

Stubb said that Ukraine's EU and NATO membership, as well as Europe's security, should be treated as non-negotiable.

Asked about Finland's potential role in any peacekeeping operation in Ukraine, the Finnish president said it was far too early to talk about boots on the ground.

"In any case, I'd much rather see drones in the air. So I think European support will essentially come more from the air and the sea than the land."

(Reporting by Max Hunder; Editing by Sharon Singleton)