Finland's defence ministry said on Thursday evening it suspected that a Russian aircraft had violated its airspace earlier on Thursday.
"Every suspected violation of airspace is taken seriously," Defence Minister Antti Hakkanen said in a ministry statement. "An investigation is underway."
There have been a series of such incidents in Finland, which shares a 1,340-kilometre (830-mile) border with Russia.
Finland suspects two Russian military aircraft of having entered Finnish airspace in May and in June, and summoned the Russian charge d'affairs at the time.
The country has been on high alert since the Kremlin sent troops into Ukraine in February 2022.
The war prompted Finland to abandon its decades-long policy of military non-alignment and it joined the NATO alliance in April 2023.
