Secretary General Jens Stoltenberg, Dec. 1 2014NATO accused Russia of posing a danger to civil aviation in the Baltic region after Stockholm protested over a Russian air force jet it said had flown too close to an airliner and had turned off one of its location instruments.

Friday’s incident off southern Sweden inflamed sensitivities over Russian air force flights in the Nordic region that have increased steeply this year, driven in part by tensions over Moscow’s role in the Ukraine crisis. Finland also expressed concern about “Dark Flights” with so-called transponder locators switched off.

“It is not only a question of increased…flights but it’s the way they’re conducting the flights. They are not filing their flight plans and they are not communicating with civilian air traffic control and they are not turning on their transponders,” NATO Secretary General Jens Stoltenberg told a news conference on Monday.

“That poses a risk to civilian air traffic. The important thing is that NATO stays vigilant and that we intercept the Russian flights.”