The Finnish defence ministry and coastguard announced the violation in the eastern Gulf of Finland in separate statements -- the latest of several recent border incidents between the two countries.

"The Russian Baltic Fleet research vessel Mikhail Kazansky crossed the external border of Finnish territorial waters" east of Helsinki early on Tuesday afternoon, the coastguard said in a statement sent to AFP.

It said the vessel travelled about 1.2 nautical miles in Finnish territorial waters and left them seven minutes later.

It said a Finnish patrol boat tried several times to contact the Russian vessel without success.

Relations between the countries, who share a 1,340-kilometre-long (830-mile) border, have worsened since Finland joined the western military alliance NATO last year, in the wake of Russia's 2022 invasion of Ukraine.

The previous territorial incident took place on June 10 when Finnish authorities said four Russian state aircraft entered Finland's airspace off the coast in the same region.

The aircraft remained in Finnish airspace for about two minutes and flew up to 2.5 kilometres into Finnish territory, the ministry said at the time.

Announcing Friday's incident earlier, Finland's defence ministry said the border guard force was investigating.

Finland closed its land border with Russia in December, accusing Moscow of trying to destabilise it by enabling undocumented migrants to enter Finnish territory.