Much has been made of reports that Russian military aircraft have penetrated U.S. airspace 16 times over the last 10 days. But the so-called incursions aren't actually a violation of any treaty, national border or military agreement, according to federal defense officials.

Russian military aircraft training in the Northwest Pacific Ocean near Alaska have caused North American Air Defense officials to scramble fighter jets to check them out recently. But the aircraft have not penetrated U.S. airspace, according to John Cornelio, NORAD's deputy director of public affairs.

The growing confusion about whether the standoff in Ukraine (which has resulted in severe financial restrictions on Russia from the U.S. and a retaliatory ban on all U.S. food products from Russia) has led to Russian military incursions into U.S. airspace may be a result of terminology.

According to NORAD, the Russian aircraft were operating over international waters but inside the Alaska Air Defense Identification Zone, an area usually extending about 200 miles from the Alaska coastline. (The zone is much smaller in areas like the Bering Strait where another nation's border is less than 200 miles away.) All aircraft entering the zone are required to submit flight plans to local air traffic control towers. Any plane spotted in the area that does not identify itself, does not have a working transponder or has not filed a flight plan is visually identified by U.S. and Canadian military aircraft.

"Over the past week, NORAD has visually identified Russian aircraft operating in and around the U.S. air defense identification zones," said Maj. Jennifer Lovett, director of public affairs for the Alaskan Command.

"While there has been a spike in activity, we assess that these flights are in keeping with the mission of routine training and exercises, and it's important to note that these Russian aircraft remained in international air space at all times," Lovett said.

Lovett would not go into detail about the numbers or types of Russian aircraft contacted inside the Alaska Air Defense Identification Zone, or how close they got to U.S. airspace, defined as an area 12 nautical miles from the coastline. Lovett would also not comment on what happens when a NORAD military aircraft scrambles to identify an unknown plane inside the identification zone.

But NORAD was firm in its statement that the Russians have not violated American airspace.

"There have been absolutely no incursions into U.S. airspace. Zero. No violations of U.S. sovereign airspace," Cornelio said.

Contact Sean Doogan at sean@alaskadispatch.com.

Correction: An earlier version of this article contained an incorrect figure for the number of nautical miles that define U.S. airspace.