Two Russian bombers, capable of carrying nuclear cruise missiles, circled the U.S. island of Guam in the Western Pacific this week, U.S. military officials told NBC News. U.S. Air Force F-15 jets scrambled from Andersen Air Force Base on Guam to intercept the bombers.

According to one military official, the Russian Bear bombers remained in international airspace, the encounter between the U.S. and Russian aircraft “stayed professional” and there was no incident. The official said it’s impossible to determine whether the Russian bombers carried any nuclear weapons.

U.S. long-range radars and satellites tracked the two bombers as they took off from northeastern Russia and headed south on a long-range flight that required “multiple refueling.” Japan also scrambled fighter jets as the bombers passed near but did not enter Japanese airspace.

U.S. military officials say “it’s highly unusual but not unprecedented” that Russian bombers would fly training missions in the vicinity of Guam. According to one official, “It wasn’t provocative but it certainly got our attention.” U.S. long-range B-52 bombers, also capable of carrying nuclear weapons, are based at Guam.

Since Vladimir Putin reclaimed the Russian presidency, U.S. officials said the number of such flights in the vicinity of the Aleutian Islands and Alaska have increased, but encounters with U.S. aircraft have remained “generally very professional.”

The two Russian Bear bombers flew near Guam at about the same time President Barack Obama delivered his State of the Union message. Military officials refused to speculate about the timing.

The interception was first reported in the Washington Free Beacon.