A Japanese Maritime Self-Defense Force submarine joined a drill last week in the South China Sea for the first time, the MSDF said Monday, signaling Tokyo's intention to keep China's muscle-flexing in the area in check and prompting an immediate rebuke from Beijing.

In a rare announcement, the MSDF said the submarine Kuroshio, along with the helicopter carrier Kaga and two destroyers, the Inazuma and Suzutsuki, conducted an antisubmarine warfare exercise in the sea last Thursday.

(Kuroshio)
[Photo from the MSDF 's website]

The submarine left an MSDF base in western Japan's Kure on Aug. 27 for the drill.

Usually, the MSDF keeps the activities of its submarines secret, except for long-term dispatches to places such as Hawaii for drills.

The three other ships were separately dispatched to the exercise area encompassing the South China Sea and the Indian Ocean for the period from Aug. 26 to Oct. 30 to join similar operations conducted by the U.S. and some Southeast Asian countries' navies.

The Kuroshio made a port call Monday at Vietnam's strategic Cam Ranh Bay facing the South China Sea, which is relatively close to the Paracel and Spratly island chains. Vietnam is at odds with China over claims to those islands.

In Beijing, Foreign Ministry spokesman Geng Shuang said in response to the drill involving the Japanese submarine that regional peace and stability should not be undermined by a country outside the region.

China claims the entire South China Sea -- with its self-declared maritime border known as the "nine-dash line" -- and has built artificial islands with military infrastructure in the waters.

The MSDF is believed to have conducted the drill on the high seas within the nine-dash line.

Japan and China launched a communication mechanism between their defense authorities in June to avert accidental clashes at sea and in the air. But some Japanese officials are concerned that there could be unintended clashes.

"We need to advance talks as early as possible to ensure (the mechanism) becomes something useful to avoid accidental clashes," a senior official at the Japanese Defense Ministry.

Other Asian countries such as Brunei, Malaysia and the Philippines also have territorial claims in the sea.

The Chinese Foreign Ministry spokesman said China is in talks with Southeast Asian countries to avoid disputes and called on countries outside the region to act prudently.