Officials believe that a Russian state-owned plane briefly crossed into Finland’s territory west of the Hanko peninsula shortly before 7 pm Saturday.
The Border Guard is investigating the incident.
In late May, two Russian planes crossed into Finnish airspace on the same day near Porvoo.
The incidents aroused a debate when it emerged that the government had been provided with unclear information, and then-premier Jyrki Katainen long held an incorrect impression of how the aircraft had been identified, for instance.
The Defence Ministry's director of communications, Max Arhippainen, declined to divulge further information to Yle about the latest incursion, or to comment on whether the process informing national leaders would be different this time.
The Russian Defence Ministry told the news agency Ria Novosti that there had been no incursion into Finnish airspace.
