Finland is prepared to close all its border crossings with Russia if necessary and has warned that Moscow could try to smuggle soldiers or war criminals into the EU among the migrants it is deliberately sending across the frontier.

Elina Valtonen, Finland’s foreign minister, told the Financial Times that if Russia intensified its operation of allowing migrants from countries such as Yemen, Iraq and Syria to cross without documents, her country could restrict the filing of asylum applications to Helsinki airport — and so exclude its checkpoints along the land border.

Finland says Russia is using the migrants to put a kind of pressure on Helsinki that falls short of outright hostilities, a method sometimes known as “hybrid” warfare or operations.

Finland first closed its busiest four crossings with Russia a week ago and was due to close three more on Friday, leaving just its northernmost border point with Russia open and processing asylum seekers.

“We have taken this step by step in order to signal to Russia that we can’t accept this hybrid operation taking place,” she added.

Valtonen endorsed a Finnish government warning that as the people crossing the border did not have documents, Russia could use the opportunity to smuggle across soldiers or those who have committed war crimes.

“It’s more of a philosophical question — we cannot have Russia decide which people come to the border, and which people come over,” she said, adding that the lack of documents complicated the process of checking people’s identities.

Russia has denied orchestrating the crossings, but experts say it is inconceivable that Moscow would accidentally allow hundreds of foreigners near its closely controlled borders.

Finland, which became the 31st member of Nato in April, regards the drive to push asylum seekers, mostly from the Middle East and Africa, across the border as the latest in a series of hybrid attacks from Russia designed to test the Nordic country.

Russia used a similar tactic in 2015-16 against Finland and Norway, with asylum seekers sent by bicycle across Arctic border crossings. Belarus, Moscow’s close ally, pushed migrants into Lithuania, Latvia and Poland in 2021.

Finland also recently suffered damage to a gas pipeline and a data cable linking it to Estonia, and has blamed a Hong Kong-registered ship with ill-defined links to Russia.

Finland received more asylum seekers from Russia in a few days this month than it has done in the rest of the year. Finnish media reports have suggested there are several hundred asylum seekers in hotels in a Russian city close to the border and officials in Finland are braced for more arrivals in its freezing north.

“In the past few weeks, we’ve witnessed Russia changing its border policy,” Valtonen said. “It is not only letting through people without documentation but there is evidence they are being helped across the border and aided with transport.”

The centre-right foreign minister said it was a “textbook” hybrid operation where Russia tested Finland’s legal system and “our response”.

Finland changed its laws last year after the Belarusian migration crisis to allow it to react quickly without invoking a state of emergency and allowing it to centralise asylum processing if necessary.

Valtonen said that Finland was prepared for “all possible scenarios” with Russia in the coming years. Russia has blamed Finland for increasing tensions by joining Nato, although western governments say it is Moscow that has raised the stakes by launching a full-scale invasion of Ukraine.

The Finnish minister noted: “If Nato posed a threat to Russia, they would not have sent all their troops away from their western border facing Finland. Nato has never been a threat to Russia, not now or in the future.”

On the pipeline damage, which also affected a Swedish-Estonian data cable, she said Finland was co-operating with China over investigations into the Hong Kong ship. “It’s possible, but not very likely, that a vessel within a timeframe of eight hours is able [unintentionally] to break two data cables and a gas pipeline,” she added.