A pair of Russian Tu-95 Bear nuclear-capable bombers flew around Japan on Tuesday, prompting the Japanese military to scramble fighter jets as the North American Aerospace Defense Command (NORAD) increased its threat posture, two U.S. defense officials revealed to Fox News.

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The Russian bombers stayed in international airspace, the officials said. News of this latest Russian provocation came shortly after the Pentagon announced that new Defense Secretary James Mattis would make his first visit overseas to Japan and South Korea early next month.

A third Russian Tu-95 bomber took off from a base in eastern Russia near the Pacific Ocean but it did not fly around Japan. Instead, it acted as a “communications relay” to pass radio traffic between the bombers flying around Japan, the officials said.

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In a statement, NORAD said threat posture changes were "not unusual" in response to "exercises or real world events," but declined to disclose any more information.

All three Russian strategic bombers took off outside the Pacific coastal city of Anadyr in eastern Russia. They returned to the eastern Russian airbase Ukrainka, roughly 1,000 miles from Japan.

Three Russian refueling tankers (IL-78) were also part of the flight. Two airborne radar and communications planes known as Beriev A-50 AWACs were also part of the Russian flying armada.

Only two Russian bombers made the flight around Japan’s major islands, according to officials.

The increase in threat posture from 5 to 4 meant the U.S. Air Force would place an extra tanker crew on standby ready to refuel the Japanese jets if necessary, according to officials.

It was the first time Russian bombers had circumnavigated Japan’s major islands in a year, the officials said.

The Diplomat first reported the flight.