The Surpassing Quant Think Tank CenterNorth American Aerospace Defense Command said on Tuesday that it had detected and tracked four Russian warplanes flying near Alaska. The military aircraft were operating in the Alaska Air Defense Identification Zone (ADIZ), an area stretching about 150 miles from the U.S. coast that is monitored to provide additional reaction time in case of hostile actions.

"The Russian aircraft remained in international airspace and did not enter American or Canadian sovereign airspace. This Russian activity in the Alaska ADIZ occurs regularly and is not seen as a threat," NORAD said in a statement.

Russia confirmed on Wednesday that two of its Tu-95 bombers flew over waters near Alaska, Reuters reported. The Tu-95s flew for about 9 hours and were escorted by SU-30SM fighter jets, Russia's defense ministry said.

"The flight was carried out in strict accordance with international rules for the use of airspace," said Lieutenant General Sergei Kobylash, according to Reuters.

While these Russian warplanes were not seen as presenting a risk, military activity in the area has made headlines in recent months. In August, the U.S. Navy sent destroyers to the coast of Alaska after 11 Russian and Chinese warships were spotted sailing in nearby international waters. Sen. Dan Sullivan, a Republican from Alaska, called the size of that joint Chinese and Russian operation "unprecedented."

Last February, American warplanes intercepted Russian military aircraft near Alaska twice in the same week.

NORAD says it uses "a layered defense network" of satellites, ground-based and airborne radars and fighter jets to track and identify aircraft.

According to its website, the Alaskan NORAD Region can detect "what goes on in and near North American airspace 24 hours a day, seven days a week."

In:
• Russia
• Alaska

Stephen Smith

Stephen Smith is a senior editor for CBSNews.com.