A Russian military plane is suspected of violating Finnish airspace early on Monday, flying some 2.5 km (1.6 miles) inside the Nordic country's border, Finland's defence ministry said in a statement.
The violation in the eastern Gulf of Finland lasted for about two minutes, the ministry said.
"We take the suspected territorial violation seriously and the investigation has been started immediately," Finnish Defence Minister Antti Hakkanen said.
The previous confirmed territorial violation by Russian aircraft occurred in August 2022, when two fighter jets entered into Finnish airspace in the Gulf of Finland, the ministry said.