4 Russian military aircraft detected in Alaska defense zone, NORAD says

Four Russian military aircraft passed through the Alaska Air Defense Identification Zone on Monday, the North American Aerospace Defense Command said.

All four aircraft remained in international airspace and did not enter either American or Canadian sovereign airspace, NORAD said in a press release. There was no intercept, it added.

"This Russian activity in the Alaska ADIZ occurs regularly and is not seen as a threat," NORAD said.

Monday's detection is the fifth such incident in September so far, according to NORAD's public statements noting detections. NORAD did not specify what type of Russian aircraft were involved. The command identified Russian IL-38 maritime patrol aircraft inside the Alaska ADIZ earlier this month.

The ADIZ begin at the limit of national airspace -- in this case that of the U.S. and Canada. Such zones require "the ready identification of all aircraft in the interest of national security," NORAD said.

The command "employs a layered defense network of satellites, ground-based and airborne radars and fighter aircraft to track aircraft and inform appropriate actions," it said in its press release.

"NORAD remains ready to employ a number of response options in defense of North America," it added.