Russia said Sunday it scrambled fighter jets to intercept two U.S. military long-range bomber aircraft that approached the Russian border over the Barents Sea in the Arctic.

“The crews of the Russian fighters identified the aerial target as a pair of U.S. Air Force B-52H strategic bombers,” Moscow’s defense ministry wrote on the social media platform Telegram, specifying that the planes scrambled were MiG-29 and MiG-31 fighters.

“As the Russian fighters approached, the U.S. strategic bombers turned away from the State Border of the Russian Federation,” the ministry said.

Russia has ramped up military operations in the Arctic Circle, including tests of advanced hypersonic missiles. Several years ago, a Russian natural gas tanker completed an experimental round trip along the Northern Sea Route, which connects Western Europe and the Atlantic Ocean to East Asia.

The U.S. routinely carries out flights over international waters. Moscow has recently responded more aggressively to the exercises, accusing the U.S. in June of using its reconnaissance drone flights over neutral waters in the Black Sea to help Ukraine strike Russian-occupied Crimea.

Last month, Moscow warned of a “direct confrontation” between Russia and NATO, and Russia’s defense minister ordered officials to prepare a “response” to U.S. drone flights over the Black Sea, in an apparent warning it may take forceful action to ward off the American reconnaissance aircraft.

Washington and Moscow have clashed before over the issue. In March 2023, a Russian Su-27 fighter jet damaged a U.S. MQ-9 Reaper drone, causing it to crash into the Black Sea. It was the first direct clash between Russian and U.S. forces since the Cold War.

A repeat of such a confrontation could further fuel tensions over the war in Ukraine.

In May, a NATO source told Reuters that scrambles of NATO jets to intercept Russian aircraft over the Baltic Sea region increased at least 20% in the first quarter of 2024.