Finland said that a Russian military aircraft violated its airspace on Monday in the first such move since the Nordic country joined the NATO alliance last year.

The plane flew in Finland’s airspace for about 2 minutes on Monday morning, the Defense Ministry said in a statement. The incident happened in the eastern part of the Gulf of Finland, with the aircraft reaching as deep as 2.5 kilometers (1.6 miles) into Finland’s territory.

“We take the suspected territorial violation seriously and have immediately launched an investigation,” Defense Minister Antti Hakkanen said. NATO Fortified

NATO controls much of the Baltic Sea after northern enlargement

The latest such incident happened in August 2022, when two Russian fighter jets flew into Finnish airspace. The Nordic nation joined the North Atlantic Treaty Organization in April 2023, just over a year after its neighbor Russia launched its full-scale war in Ukraine.

Finland guards more than 1,300 kilometers of border against Russia — a stretch that now makes up about a half of NATO’s Eastern flank.