The British Royal Air Force scrambled fighter jets to intercept a pair of Russian Blackjack bombers as they encroached on airspace the UK considers an “area of interest” on Monday morning.

Two RAF Typhoon fighters out of Lossiemouth in Scotland were launched to intercept and escort the two Russian Tupolev Tu-160 Blackjack bombers as they came to within 50 miles of UK airspace. Two more Belgian F-16s were also scrambled to intercept the long-range bombers in the same incident.

“We can confirm that Quick Reaction Alert Typhoon aircraft from RAF Lossiemouth scrambled to monitor two Blackjack bombers approaching the UK area of interest.” An RAF spokesman said following the incident.

“The Russian aircraft were initially monitored by a variety of friendly nation fighters and subsequently intercepted by the RAF in the North Sea. At no point did the Russian aircraft enter sovereign UK airspace.”

Russian officials stated that the bombers were flying a training mission that took them over the Barents, Norwegian, and North seas, and that their aircraft stayed over international waters throughout the 13 hour flight. British officials did not contest the Russian account, but it is considered an international norm to intercept and escort potentially offensive bombers as they approach a nation’s airspace.

These kinds of intercepts are not at all uncommon, as Russian bombers probe the outer defensive perimeters of diplomatic opponents around the globe. They have, however, grown increasingly frequent in recent years, as Russia has pushed to re-establish themselves as a global military power after the collapse of the Soviet Union in the 1990s.

The Tupolev Tu-160 Blackjack bomber is often compared to America’s B-1B Lancer thanks to its variable-sweep wing and supersonic flight capabilities. Like the Lancer, the Blackjack’s flight characteristics are more like that of a fighter jet than a heavy payload bomber, with a purported maximum speed that exceeds Mach 2, which if true, would make these bombers faster than the Typhoon fighters sent to intercept. The Blackjack, however, does differ from the Lancer in one very important way: unlike America’s supersonic bomber, the Blackjack is capable of being equipped with nuclear weapons. Russia’s military boasts only 27 total Blackjack bombers, with only 16 believed to be operational in 2016.

Russia recently announced plans to launch another construction cycle for a newly updated version of the Tupolev Tu-160, dubbed the Tu-160M2.  The first operational supersonic bomber of this new generation is expected to take to the skies later this year, with full-scale production slated to begin in 2021.