Russian fighter jets were caught escorting two nuclear-capable bombers off the coast of Alaska on Tuesday - marking the second such incident this month, according to United States officials.
The Russian military formation included two Tu-95 "Bear" bombers and a pair of Su-35 "Flanker" fighter jets, officials said.
The Russian warplanes did not enter US or Canadian sovereign airspace, the statement added.
It's the second time this month that Russian aircraft have been intercepted in Air Defense Identification Zone, Hennessy said.
North Atlantic Treaty Organisation claims Russian warplanes regularly fly without respecting worldwide safety norms, such as responding to air traffic control and requests to identify themselves.
On May 11, US jets shadowed a pair of Tu-95s as they flew in the zone, which extends 200 miles from the coast, in the Bering Sea north of the Aleutians.More news: Digger: Klopp doesn't need silverware this season
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The aircraft were "intercepted and monitored" by the USA jets until they left the zone, heading west.
No other details of the intercept were disclosed.
A previous interception of bombers occurring on September 1 involved bombers without any Russian fighter jet escorts, CNN noted.
The bombers and jet fighters also were likely testing US air defenses to gauge NORAD responses and how quickly they respond to incursions in protected airspace. The bombers didn't enter Canadian or USA airspace, NORAD said.
The latest Bear bombers incursion coincided with the start of Russian war games known as Vostok-18 that Russian officials have said are the largest since 1981.
The drills involve almost 300,000 Russian troops along with 1,000 Russian aircraft, 36,000 tanks and other combat vehicles, the news agency said.