MOSCOW, December 12 (RIA Novosti) - NATO fighters have trailed two Russian strategic bombers on a patrol mission over the North Sea, a Russian Air Force spokesman said on Friday.

Col. Vladimir Drik said two Tu-160 Blackjack bombers, on a 13-hour mission Thursday night, were closely followed by Norwegian F-16 and British Tornado fighters.

The shadowing of Russian warplanes by NATO fighters has been common practice since Russia resumed strategic bomber patrol flights over the Pacific, Atlantic, and Arctic oceans last August.

Russia has stressed that regular patrol missions by its strategic bombers pose no threat to other countries, and it always gives notice of upcoming patrols.

The Air Force has said the main purpose of these missions is to hone the pilots' long-range flying skills and practice aerial refueling.