NATO ground forces on Saturday started operations aimed at boosting defences around Sweden and Finland, two of its newest members, the alliance said.

Following Russia’s all-out 2022 invasion of Ukraine, the two Nordic countries abandoned decades of military non-alignment to join NATO. Finland entered the alliance in 2023 and Sweden did likewise the following year.

The region around the two countries, part of NATO’s northeastern flank, “is one of the most strategically significant and environmentally challenging areas in the world,” the US general who is NATO’s Supreme Allied Commander Europe, Alexus Grynkewich, said in a statement.

Sweden and Finland lie on the Baltic Sea, the waterway used by Russian warships heading to or from Saint Petersburg or the Russian exclave of Kaliningrad.

Finland, which shares a border with Russia, also fought two wars against the Soviet Union during World War II.

NATO in 2024 decided to establish a new multinational military presence in Finland called the Forward Land Forces (FLF) Finland, designed to act as a rapid-reaction unit.

That force, which began operations on Saturday, includes a Swedish battle group.

NATO has other similar land units in Bulgaria, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia.