In the latest of several border incidents, the vessel is suspected to have entered Finnish waters in the eastern Gulf of Finland on Friday afternoon, the Finnish defence ministry said in a short statement.

It did not identify the vessel or say what kind it was.

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

The previous confirmed territorial violation took place on June 10 when four Russian state aircraft entered Finland's airspace off the coast east of Helsinki.

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.

The Border Guard was investigating Friday's incident and would provide further information as the investigation progressed, the statement said.