SEOUL, South Korea (AP) — South Korea said Tuesday that Russian warplanes entered its air buffer zone unannounced, and that it responded with unspecified "tactical action," a term that usually refers to the scrambling of fighter jets to chase away unauthorized foreign aircraft.

South Korea's Joint Chiefs of Staff said in a statement that the move was aimed at preventing accidental clashes along its air defense identification zone, but didn't provide more details.

The South Korean military didn't confirm Russian media reports that it scrambled F-16 fighter jets in response to two Russian Tu-95 bombers escorted by a Sukhoi Su-30 fighter jet flying over waters between the Korean Peninsula and Japan.

The incident came a day after South Korea and the United States began their biggest combined military training in years in a response to North Korea's nuclear threat. The Ulchi Freedom Shield exercises, which continue through Sept. 1, involve aircraft, warships and tanks and potentially tens of thousands of troops.

Air defense identification zones usually expand beyond a country's territory to allow more time to respond to potentially hostile aircraft. Military planes entering another country's air defense identification zone are required to notify it in advance.

Russian and Chinese warplanes have often entered South Korea's air defense identification zones in recent years as they flex their muscles amid an intensifying competition with the United States.

In 2019, South Korea said its fighter jets fired hundreds of warning shots toward a Russian military plane that it said twice violated its national airspace off its eastern coast. Russia denied that its aircraft entered South Korea's territory.