Airspace over Western Pacific waters near Japan continues to heat up at a moment of the highest tensions in decades between Beijing and Tokyo.

Tuesday saw Japan and South Korea dispatch fighter jets in response to a joint patrol by Russian and Chinese bombers over the Asia-Pacific region, the countries' militaries confirmed.

The Joint Chiefs of Staff in Seoul described that seven Russian and two Chinese aircraft entered South Korea's Air Defense Identification Zone (KADIZ) at approximately 10am local time (01:00 GMT) on Tuesday.

While the zone is not strictly speaking sovereign airspace, aircraft are expected to identify themselves to South Korean authorities. South Korea in response deployed "fighter jets to take tactical measures in preparation for any contingencies."

Russia's Defense Ministry (MoD) had confirmed its Tu-95MS strategic bombers and China’s H-9 strategic bombers conducted the eight hour flight over the Sea of Japan, the East China Sea and the Western Pacific - but that at no time was any country's airspace violated, and that it was done according to international law.

 "At certain stages of the route, the strategic missile carriers were accompanied by fighters from foreign countries, the MoD acknowledged.

Chinese J-16 fighter jets, two Russian Su-30 fighters and an A-50 early-warning aircraft provided cover for the bombers at various parts of the patrol, it was also disclosed.

But South Korea has still lodged a formal diplomatic protest, which one Seoul official saying, "Our military will continue to respond actively to the activities of neighboring countries’ aircraft within the KADIZ in compliance with international law."

Perhaps the firmest and most provocative statement came from Japan. Japanese Prime Minister Sanae Takaichi last month made statements saying Tokyo has the right to defend Taiwan if the self-ruled island is invaded by China. This sparked outrage in Beijing, which has been flexing its economic and military might, in a series of punitive measures.

Watch: Russian and Chinese bombers over the Western Pacific:

Japanese Defense Minister Shinjiro Koizumi wrote on X on Wednesday of the joint Russia-China bomber patrol, "These repeated joint bomber flights by Russia and China represent an expansion and intensification of their military activities around Japan."

"They clearly indicate deliberate acts of intimidation directed toward our country and constitute a serious concern from the standpoint of Japan’s national security," he added.