Russian surveillance aircraft entered the Alaskan Air Defense Identification Zone twice in two days, the North American Aerospace Defense Command said Tuesday.
The Alaska region of the defense command, commonly known as NORAD, detected the aircraft, which "remained in international airspace and did not enter American or Canadian sovereign airspace," according to a news release.
An air defense identification zone is a self-declared area of airspace surrounding a country or territory within which it will seek to identify foreign military aircraft. Although the zones have no basis in international law, breaching another territory’s zone is seen as an act of aggression.
NORAD uses a layered defense network of satellites, ground-based radars, airborne radar and fighter aircraft to identify other aircraft and to come up with appropriate actions.
"We remain ready to employ a number of response options in defense of North America and Arctic sovereignty," the agency said in a statement.
Russia launched a wide-ranging attack on Ukraine in February. On Saturday, hundreds of thousands of civilians still left in Donetsk, the center of Russia's latest attack, were warned that they needed to evacuate while there is still time. Officials in Donetsk said that more than two-thirds of civilians have already fled but that an estimated 350,000 remain.
Russia launched its attack on Donetsk after it seized control of Luhansk last month. Gaining control of both could mean a major victory for the Kremlin and the possibility that the war might end with its slicing off a large and crucial chunk of its neighbor’s territory.