WASHINGTON: The USS Ronald Reagan aircraft carrier scrambled four fighter jets to intercept approaching Russian warplanes as it carried out a military exercise on Tuesday in the Sea of Japan, US military officials said on Thursday.

The two Russian TU-145 "Bear" jets came as close as a nautical mile from the carrier and were flying at a low-altitude, about 500 feet above sea level, the officials said.

TU-145 Bear is a long-range anti-submarine warfare plane and a variant of the TU-95 Bear strategic bomber.

The incident, although unusual, was characterised by the Pentagon as "safe." "There was nothing to indicate they were posing a direct threat," said Pentagon spokesman Captain Jeff Davis.

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The US Navy was carrying out an exercise with South Korean ships in international waters at the time of the incident.

At the White House, spokesman Josh Earnest noted that the United States had previously raised concerns about unprofessional conduct by Russian military aircraft, including incursions into Turkish airspace in recent weeks.

"This was a little bit different than that. These are international waters," Earnest said.

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