South Korea says its warplanes fired warning shots at a Russian surveillance plane that entered its airspace above the Sea of Japan on July 23.
The plane twice entered the airspace over an island, called Dokdo by South Korea and Takeshima by Japan, which is occupied by Seoul but also claimed by Tokyo.
South Korea's Ministry of Defense said it scrambled fighter jets in response and fired 360 machine-gun rounds.
"We take a very grave view of this situation and, if it is repeated, we will take even stronger action," South Korean national-security adviser Chung Eui Yong said in a complaint lodged with Nikolai Patrushev, secretary of the Security Council of Russia.
South Korea has also summoned Russia's acting Deputy Chief of Mission Maksim Volkov and Chinese Ambassador Qiu Guohong in protest.
Japan said on July 23 that it had also scrambled warplanes to intercept Russian and Chinese planes.
Japan, like South Korea, identified two Chinese H-6 bombers and two Russian Tu-95 bombers flying over the strait between the countries.
Russia's Defense Ministry said it had conducted its first joint long-range air patrol with China in the Asia-Pacific region and that the flight was not aimed at another country.
Lieutenant-General Sergei Kobylash, commander of the Russian military's long-range air forces, said at a news briefing in Moscow on July 23 that there "was no violation of either South Korean or Japanese airspace."
He said the "South Korean jets acted unprofessionally," while denying that their warplanes had fired warning shots, otherwise "an immediate and adequate response would have ensued."
It accused the South Korean aircraft of carrying out dangerous maneuvers.
"The South Korean military took tactical action including dropping flares and firing a warning shot," the Defense Ministry statement said.
After leaving South Korean airspace, the Russian aircraft reentered 20 minutes later, prompting a second round of warning shots by South Korea's Air Force, Seoul said.