Chinese and Russian naval vessels have passed together through the Osumi Strait off Japan's southwestern prefecture of Kagoshima, the Defense Ministry said Saturday.

It is the first time the Japanese ministry has confirmed a flotilla of Chinese and Russian vessels going through the strait, located between the Osumi Peninsula and Tanegashima Island.

Chinese (R) and Russian naval vessels are spotted sailing in two parallel lines in the waters south-southeast of Danjo Islands, southwestern Japan. (Photo courtesy of Japanese Defense Ministry)(Kyodo)

With the passage, the flotilla almost made a circle around the Japanese archipelago, prompting the ministry to exercise vigilance against the unusual activity of the two countries.

After transiting the strait, the warships entered the East China Sea, according to the ministry. On Monday, they passed through the Tsugaru Strait, located between Japan's main island of Honshu and Hokkaido to the north, also marking the first such move.

The warships are believed to have taken part in a joint naval drill in the Sea of Japan conducted by the two countries in mid-October.

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