A total of four Chinese and Russian bombers on Tuesday made a joint flight above waters near Japan, the Japanese Defense Ministry said, with its Air Self-Defense Force scrambling fighter jets in response.
While Japan's airspace was not violated, the ministry conveyed its grave concerns to China and Russia through diplomatic channels, viewing the move as a clear show of force.
Recently, China and Russia have been engaging in joint military operations more actively in an apparent bid to counter the international order led by the United States and other Western nations.
Two Chinese H-6s joined two Russian Tu-95s above the Sea of Japan and flew together to the East China Sea, the ministry said, adding that the bombers were joined by what were believed to be two Chinese fighters over the waters.
The South Korean military's Joint Chiefs of Staff said eight military airplanes -- four each from China and Russia -- intruded into the Seoul-designated air defense identification zone the same day.
South Korea flew fighter jets in response and the Chinese and Russian airplanes, which included bombers, did not enter South Korea's airspace, it said.
The zone serves as a national defense perimeter used to judge whether the scrambling of fighters is needed when foreign aircraft enter without prior notification.
China and Russia also carried out a joint aerial patrol over the Sea of Japan and the East China Sea the same day, according to the Chinese Defense Ministry.
The sixth joint patrol between the two countries comes amid increased military cooperation between Beijing and Moscow.
Chinese and Russian bombers also made joint flights above waters near Japan in November last year.