NATO jets intercepted six Russian aircraft flying over the Baltic Sea without transponders or a flight plan over the past two days, the Latvian Air Force reported late on Sept. 21.

NATO has been forced to scramble fighter jets to intercept five Russian military aircraft over the Baltic Sea. The Russian planes were flying without flight plans or active transponders, according to the Latvian Air Force.

NATO troops, vessels and aircraft took to the frigid North Atlantic Ocean last month to sharpen their skills for a potential future war at sea.