Moscow (CNN) Russian President Vladimir Putin and Chinese President Xi Jinping sent a clear message on Tuesday: They are ready to test the limits of their budding military partnership in the Pacific.

Things escalated dramatically. According to South Korea, two Chinese H-6 bombers passed into Seoul's Air Defense Identification Zone, joined by two Russian Tu-95 strategic bombers. South Korea's Joint Chiefs of Staff claimed they fired warning shots at a Russian A-50 command and control military aircraft that twice violated their airspace.

Japan's Ministry of Defense backed up South Korea's claims, saying the A-50 intruded on Japan's airspace while the Russian and Chinese bombers flew around Japan. (The island area flown over in the incident is claimed by South Korea and Japan.)

Moscow disputes Seoul's account, claiming that South Korean military jets dangerously intercepted two of its bombers over neutral waters. Later on Tuesday, after reports of the midair confrontations emerged, the Russian military said its aircraft had taken part in a "joint patrol" with Chinese long-range aircraft.

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