Four F-22 Raptor fighter jets and an E-3 airborne early warning and control aircraft intercepted four Russian bombers and two Russian fighters flying off the coast of Alaska on  Monday.

According to the North American Aerospace Defense Command (NORAD), the Russian aircraft were spotted in the Alaskan Air Defense Identification Zone (ADIZ), a buffer that lies in international airspace. NORAD monitors the airspace and scrambles jets when unauthorized aircraft enter it.

Russia has conducted several missions within the ADIZ in recent years. In the latest incident, two Russian Tupolev Tu-95 bombers were first detected, at which point a pair of F-22 Raptors were scrambled to make the intercept and escort them out of the area.

Later Monday, two additional Tu-95 bombers, this time accompanied by a pair of Su-35 fighters, were also spotted on radar. Two additional Raptors were sent up to deal with the situation. The E-3, a communications and radar plane, kept tabs on the entire episode.

“NORAD’s top priority is defending Canada and the United States,” Gen. Terrence J. O’Shaughnessy, the NORAD commander, said. “Our ability to deter and defeat threats to our citizens, vital infrastructure, and national institutions starts with successfully detecting, tracking, and positively identifying aircraft of interest approaching U.S. and Canadian airspace. NORAD is on alert 24 hours a day, seven days a week, 365 days a year.”

Russia has also sailed spy ships off the East Coast of the U.S. in recent years.