Fighter jets from South Korea and the United States intercepted two Russian warplanes after they flew near a US aircraft carrier operating off the Korean peninsula, officials said Thursday.

White House spokesman Josh Earnest said the USS Ronald Reagan -- a massive, nuclear-powered supercarrier -- was involved in a military exercise with South Korean partners when two Russian Tu-142 Bear aircraft flew past the ship.

"These Russian aircraft were intercepted first by Korean military aircraft that were operating in the region," Earnest said. Four American F/A-18s were then mobilized.

Earnest sought to downplay the incident in the Sea of Japan (East Sea), calling it "not a particularly threatening encounter" and noted that the USS Ronald Reagan was operating in international waters at the time.

"This is a particular situation that did not result in a significant confrontation," he said.

The two Russian Tu-142 Bear aircraft were flying about a mile from the carrier at an altitude of 500 feet (150 meters) on Tuesday, Pentagon spokesman Captain Jeff Davis said.

He said there was no evidence the Russian planes posed a direct threat. Tu-142 Bears are primarily reconnaissance and anti-submarine aircraft.

Still, the carrier scrambled four F/A-18 fighters to intercept and escort the Russian aircraft, he said.

One of the US ships accompanying the USS Ronald Reagan tried to hail the Russian aircraft by radio but did not receive a response, he added.

"It's standard operating procedure for US planes to escort any aircraft that are flying anywhere in the vicinity of US Navy ships," Davis said. "The interaction was characterized as safe."

"Any time there are aircraft that are operating in close proximity to a US Navy ship, particularly an aircraft carrier, we are going to take action to launch and make sure we are tracking it very closely," Davis said.

He said this kind of incident is not unprecedented, noting: "It doesn't happen frequently but this did occur."

The incident comes after Russia and the United States on October 10 signed a memorandum of understanding that establishes protocols for pilots flying over Syria.

Both Russia and a US-led coalition are conducting separate bombing campaigns in the war-torn country. Though they are mainly operating in different regions, officials are worried about planes crashing into each other in the sky.