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WARSAW, Poland — Some 9,000 troops from 20 NATO countries have been participating this month in military exercises in the Baltic Sea region, which has become strategically sensitive following Russia's invasion of Ukraine.

Sweden, which had joined the drills in the past, took part in the Baltops exercises for the first time in June as a full NATO member after joining the trans-Atlantic military alliance earlier this year. The weeks of training include sea mine sweeps, submarine detection, landings and medical response to mass casualty situations.

Their goal is to enhance interoperability of the forces and to highlight the allied commitment to joint security, officials said.

The exercises by navy, air force and ground troops are being held on the Baltic Sea, as well as in Sweden and its strategic island of Gotland, and in Lithuania, Poland and Germany. They will run through Thursday and include some 50 navy ships and 45 aircraft and helicopters.

The drills are organized by NATO's Naval Striking and Support Forces and the U.S. Navy's 6th Fleet.

Major gas pipelines run across the Baltic seabed from Russia and Norway to Germany, Poland and other European nations, making it a highly sensitive region since Russia invaded Ukraine in 2022 and increased its hostile activity in the Baltic Sea area.

''The dynamic challenges of the Baltic Region demand a refined, precise, and efficient amphibious capability; and that is exactly what we conducted in Sweden today. The landing location was intentional: NATO's presence on Gotland Island is vital to protecting the security and stability of the Baltic Sea,'' said U.S. Marine Corps Brig. Gen. Andrew T. Priddy, NATO's Naval Striking and Support Forces chief of staff.