▶ Watch Video: Questions swirl about purpose of flying “objects” shot down over U.S., Canada

Two American F-16 warplanes intercepted four Russian aircraft near Alaska, the joint US-Canadian North American Aerospace Defense Command (NORAD) said Tuesday. The “routine” intercept of the Russian planes — which included Tu-95 bomber and Su-35 fighter aircraft — occurred Monday, NORAD said in a statement.

“Russian aircraft remained in international airspace and did not enter American or Canadian sovereign airspace,” it said, adding that such Russian activity “occurs regularly and is not seen as a threat, nor is the activity seen as provocative.”

The Air Defense Identification Zone, or ADIZ, is a perimeter in which air traffic is monitored beyond the border of national airspace to provide additional reaction time in case of hostile actions.

U.S. warplanes stationed in North America have seen rare offensive action this month, shooting down an alleged Chinese  spy balloon  and three unidentified objects. U.S. officials said Tuesday that intelligence officials were tracking the spy balloon that was shot down since it lifted off from the south coast of China.

“NORAD also assessed that this Russian flight activity is in no way related to recent NORAD and U.S. Northern Command operations associated with airborne objects over North America during the last two weeks,” the command said.

Interceptions of Russian aircraft in the area — which is close to Russia’s far eastern border — are relatively frequent.

In October, U.S. F-16 warplanes intercepted two Russian bombers in international airspace near Alaska and in September, NORAD said it detected two Russian maritime patrol aircraft in the ADIZ.,

NORAD says it uses “a layered defense network” of satellites, ground-based and airborne radars and fighter jets to track and identify aircraft.

According to its website, the Alaskan NORAD Region can detect “what goes on in and near North American airspace 24 hours a day, seven days a week.”

“Aerospace control requires capabilities to intercept, shadow, escort, divert, direct landings, and if necessary, use force up to and including the destruction of airborne objects,” the command says.