EU chief Ursula von der Leyen said Friday that Russia was now focusing its hybrid attacks on neighbouring Finland, using migrants to try to destabilise the country.
The Nordic nation closed its eastern border in mid-December after nearly 1,000 migrants had arrived without a visa through its border crossings with Russia since August.
The two neighbours share a 1,340-kilometre (830-mile) border, and Helsinki has said the surge in asylum seekers has been orchestrated by Russia, a charge that Moscow has denied.
"Since the hybrid attack launched by Belarus in November 2021 against Latvia, Poland and Lithuania, we all know how Putin and his allies instrumentalised migrants to test our defences and to try to destabilise us," von der Leyen told reporters on Friday.
"Now, Putin is focusing on Finland."
Belarus in 2021 orchestrated an influx of migrants to neighbouring Poland, Lithuania and Latvia, leading to a serious deterioration in relations between the European Union and Minsk.
Von der Leyen was speaking after meeting Finland's Prime Minister Petteri Orpo in the Finnish town of Lappeenranta, some 30 kilometres (19 miles) from the Russian border, to discuss "what Finland and the EU can do to prevent instrumentalised migration to Finland's eastern border", according to a statement.
The closure of Finland's eight border stations was extended several times and in April the government said it would remain closed "until further notice", since the situation remained unchanged.
The EU chief said Russia's hybrid attack "is no doubt in response to your firm support of Ukraine and your accession to NATO."
Finland's relations with Russia soured after the 2022 invasion of Ukraine.
Moscow warned of "countermeasures" after Finland joined NATO in April 2023, reversing its decades-long policy of military non-alignment.
In addition to the total border closure, Finland is currently preparing legislation aimed at restricting migration to tackle the phenomenon.
