Updated

U.S. and South Korean fighter jets scrambled to turn back a Russian bomber that approached a U.S. aircraft carrier during training exercises, South Korean and U.S. officials said Thursday.

The Russian plane flew close to the USS Nimitz in waters off South Korea's eastern coast Wednesday, but retreated shortly after the fighter jets approached, an official at the South Korean Joint Chiefs of Staff said on condition of anonymity, citing policy.

The official refused to provide details of the fighter jets involved.

Yonhap news agency quoted an unidentified military official as saying two F/A-18 Super Hornet fighters from the carrier and four South Korean F-16 jets were deployed to intercept the Russian plane.

The Russian navy confirmed that a Tu-142 anti-submarine aircraft flew over the American carrier, calling it a routine mission over the open sea.

"Attempts by U.S. officials to portray almost every flight of the Russian military aviation, including our naval aviation, over the world ocean as some sort of breach are appalling," Igor Dygalo, assistant to the navy commander in chief, said, according to Russia's Interfax-AVN news agency.

In February, U.S. fighter planes intercepted two Russian bombers — one directly flying over the Nimitz in the western Pacific ocean.

In Washington, a defense official downplayed the significance of the latest incident.

"We don't view this activity as threatening or of concern," the official said on condition of anonymity because of the sensitivity of the issue.

The official said it was standard operating procedure for Navy aircraft to escort a plane flying near its ships.

To get close to the U.S. carrier, the Russian plane intruded into a South Korean-controlled air defense zone above the open sea, Yonhap reported.

The zone does not belong to South Korea's aerial territory but was demarcated by the U.S. military a year after the Korean War broke out in 1950 as part of efforts to prevent accidental aerial clashes among regional powers.

In recent years, discord between the U.S. and Russia has grown over American plans to build a missile defense network and expand NATO membership. Russia has sought to bolster political and trade ties with countries in Asia and the Middle East to counter U.S. clout.

The U.S. stations 28,500 troops in South Korea in a legacy of the Korean War, which ended with an armistice, not a peace treaty. American and South Korean troops regularly stage joint exercises to maintain their ability to deter any North Korean attack.