In an interview with Reuters, Stubb promised unconditional support for Ukraine and ruled out an improvement in Finland's relations with Russian President Vladimir Putin until Moscow stops the war against Kyiv.

Stubb, 55, leads opinion polls before Finland's Jan. 28 presidential election, which precedes presidential elections this year in neighbouring Russia and the United States.

The former prime minister hopes to succeed Sauli Niinisto, who is retiring at 75 after two six-year terms, having been nicknamed "the Putin whisperer" for his role in keeping lines open with Russia's leader before the 2022 invasion of Ukraine.

Helsinki's relations with Moscow deteriorated after the invasion and sank further when Finland, in an historic break with tradition prompted by the invasion, joined NATO last April.

Stubb signalled clearly that he would lean towards the West if elected president and said it was "very important that we in Europe take care of our own defence."

"So in that sense, I'm very much along the lines of the current Finnish president, Sauli Niinisto, who said that we need a more European NATO," he said in the interview.

"I think the Americans will not leave us alone (on our own), but it's always useful to be prepared in the situation whereby we have to take more responsibility for our own defence."

CALL TO END UKRAINE WAR

Stubb expressed no concern about whether Trump will be re-elected, despite a high-level European official saying this week that Trump had stated when he was president that the U.S. would never help Europe if it came under attack.

"Americans understand why we (Finland) are important and in that sense no matter who is elected as the U.S. president will understand that as well," Stubb said.

Last month, Finland, which is in the European Union as well as NATO, signed a defence cooperation agreement with Washington granting the U.S. military broad access across the Nordic country, which shares a 1,340-km (830-mile) border with Russia.

Finland closed the border with Russia late last year to stop asylum seekers entering the country, and said Moscow had orchestrated the inflow of people, a charge the Kremlin denies. The closure had been set to end on Jan. 15, but was extended this week until Feb. 11.

"Politically, there will be no relations with the president of Russia or with the Russian political leadership until they stop the war in Ukraine," Stubb said.

Making clear this did not mean severing diplomatic ties, he added: "They are the aggressor, so in that sense there is no political relationship. On a pragmatic level, obviously our border guards continue to cooperate and our diplomats continue to cooperate, but there is no Russian pillar of foreign policy."

Stubb, a member of the centre-right National Coalition Party who describes himself a moderate, has topped most opinion polls in recent months. The latest poll, published by the Helsingin Sanomat newspaper on Dec. 26, put him on 24% support among respondents and his main opponent, liberal Green Party member Pekka Haavisto, on 22%.

A second round run-off will be held on Feb. 11 if no candidate wins more than 50% of the vote.

(Reporting by Anne Kauranen, Editing by Timothy Heritage and Andrew Heavens)

By Anne Kauranen