The U.S. detected and tracked Russian military aircraft that entered the Air Defense Identification Zone off of Alaska on Monday, the U.S. military said.

The ADIZ is an area that stretches out 150 miles from U.S. territory, where the U.S. requires aircraft to have their transponders on or to identify themselves.

"This Russian activity in Alaskan ADIZ occurs regularly and is not seen as a threat," the North American Aerospace Defense Command said in a press release.

There was no NORAD intercept on Monday, the military said, adding that NORAD tracked the aircraft as they flew through the ADIZ without entering U.S. or Canadian airspace.

U.S. territorial airspace and waters begin 12 nautical miles from the coastline.