As many as 12 Russian military aircraft were spotted Wednesday near Latvia’s sovereign airspace in the Baltic region of Eastern Europe, a statement by the Latvian Armed Forces said. Russia has flown hundreds of aircraft and positioned dozens of ships during the last 18 months near the territory of the former Soviet republics of Latvia, Estonia and Lithuania, prompting alarm across Eastern Europe and inside NATO.

"Patrol aircraft have identified on Wednesday four Mikoyan MiG-31, four Sukhoi Su-24, three Antonov An-26 and one Ilyushin IL-76 aircraft of the Russian air force over the international waters of the Baltic Sea near Latvia’s external sea border," the statement said.

While the flights were often over international waters, many of Russia’s aircraft do not fly with flight transponders on, making it nearly impossible for other aircraft and air traffic control to locate them. This can be dangerous for commercial aircraft flying in the area.

Sweden and Denmark summoned Russian ambassadors in December to complain about one such incident when a Russian jet traveled in a commercial flight path between Copenhagen and Sweden. Russia denied it has been a hazard to commercial flights.

In light of this threat, NATO could employ what’s known as the Baltic Air Policing mission, which is a group of alliance members that monitor the otherwise unprotected skies of the three Baltic states, none of which has an air force.

Russian Ambassador to Latvia Alexander Veshnyakov met in January with Latvian government officials to discuss the issue. “All flights of the Russian Air Force and the movements of warships were made in strict accordance with international legal norms,” Veshnyakov said, before adding the maneuvers of the Russian armed forces "were conducted transparently within the framework of international agreements and arrangements." 

In June, a U.S. sailor recorded footage of Russian jets flying over a U.S.-led NATO mission in the Baltic Sea.