Photo/Illutration A fleet of Chinese naval vessels, right, and Russian naval vessels navigates in waters off the Japanese archipelago in late October. Chinese naval vessels were also seen carrying helicopters. (Provided by the Defense Ministry’s Joint Staff)

Chinese and Russian naval vessels for the first time passed through a second strait in waters off the Japanese archipelago simultaneously on Oct. 22.

A fleet of 10 naval vessels consisting of five from each country traversed the Osumi Strait, located between Kyushu and Tanegashima island, into the East China Sea, Japan’s Defense Ministry announced the following day.

The same fleet on Oct. 18 moved through the Tsugaru Strait, separating the Japanese islands of Honshu and Hokkaido, into the Pacific Ocean, meaning it has now traveled halfway around the Japanese archipelago.

As well as being the first time Chinese and Russian naval vessels have passed through the two straits at the same time, it is also unusual for such a large number of vessels to simultaneously sail through a strait in waters off the Japanese archipelago.

The move was an apparent attempt to put military pressure on Japan, according to a Japanese government source.

China and Russia are believed to be trying to counter repeated joint military drills Japan is conducting with the United States and other countries.

The 10 vessels were first spotted on Oct. 18 in waters about 110 kilometers southwest of Okushiri island in Hokkaido, according to the Defense Ministry. They then sailed east into the Pacific Ocean through the Tsugaru Strait.

Two days later, the vessels were seen navigating in the sea about 130 km east of Cape Inubosaki in Chiba Prefecture.

On Oct. 21, they were spotted in the Izu island chain, south of Tokyo, and helicopters simultaneously took off from Chinese and Russian frigates and landed on them. Japan’s Air Self-Defense Force scrambled fighter jets to respond to a possible intrusion by those helicopters into the country’s airspace.

The following day, the 10 vessels were seen sailing in waters about 180 km south of Cape Ashizuri in Kochi Prefecture and moved westward into the East China Sea through Kagoshima Prefecture's Osumi Strait the same day.

On Oct. 23, the vessels were spotted in the sea about 130 km south-southeast of the Danjo islands in Nagasaki Prefecture. A helicopter was also seen taking off from a Chinese navy vessel and landing on it.

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