First, it was a suspected Chinese surveillance balloon. Then, there were three high-altitude unidentified flying objects. Now, Russian aircraft.

The North American Aerospace Defense Command said it intercepted four Russian aircraft operating within the Alaska Air Defense Identification Zone on Monday.

In a news release posted Tuesday on NORAD's Twitter account, NORAD said activity involving Russian aircraft around the ADIZ "occurs regularly and is not seen as a threat, nor is the activity seen as provocative." Russia is only 55 miles away from Alaska across the Bering Strait.

"Russian aircraft remained in international airspace and did not enter American or Canadian sovereign airspace," said NORAD, which added it anticipated the Russian maneuvers and was prepared to intercept the aircraft.

NORAD said the Russian aircraft included the TU-95 BEAR-H strategic bomber and the SU-35 fighter jet. It said two U.S. F-16 fighter jets, supported by two F-35 fighter jets, an E-3 Sentry AWAC and two KC-135 Stratotankers, intercepted the Russian aircraft.

"Since Russia resumed out-of-area Long Range Aviation activity in 2007, NORAD has seen a yearly average of approximately six to seven intercepts of Russian military aircraft in the ADIZ," NORAD said. "These numbers have varied each year from as high as 15 to as low as zero."

NORAD said it routinely monitors foreign aircraft movements through a layered defense network of satellites, ground-based radars, airborne radars and fighter aircraft and, as necessary, escorts them from the ADIZ.

"We remain ready to employ a number of response options in defense of North America and Arctic sovereignty," NORAD said.

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