F-22 Raptor fighters from NORAD intercepted and visually identified the long-range Tupolev Tu-95 "Bear" bombers overnight Tuesday, said the joint US-Canadian command, charged with aerospace warning and control for North America.

The four-engine Cold War-era turboprop bombers, which can carry nuclear weapons, were escorted by two Russian Su-35 fighters, NORAD said in a statement Thursday, adding that the Russian planes stayed in international airspace and never penetrated the US or Canadian zones.

NORAD jets followed the Russians until they left the air defense identification zone, a perimeter in which the military surveils air traffic, and which extends for about 200 miles (320 kilometers) off Alaska.

The incident took place during Russia's largest-ever military drills, Vostok-2018 with nearly 300,000 troops and all types of military equipment in eastern Siberia.

NORAD commander General Terrence O'Shaughnessy said he did not see the air incident as "directly part of Vostok although it is very much related to it."

In May, US fighter jets also intercepted two Russian Bear bombers in international airspace off western Alaska.

In April 2017, NORAD and the Pentagon said Tu-95 bombers were spotted in international airspace on three occasions -- twice near the Aleutians and once near mainland Alaska and Canada.

That was the first sighting of such Russian long-range bombers around Alaska in about two and a half years, a Pentagon spokesman said at the time.

Tensions between Russia and the United States and its NATO allies are running at levels not seen since the Cold War.