TOKYO - A total of 11 Chinese and Russian navy ships sailed through waters near Japan's southern islands of Okinawa Prefecture on Thursday, prompting the Japanese government to express "grave concerns" over what it calls a show of force by its neighbors.

The vessels headed into the East China Sea after passing through waters between the prefecture's main island of Okinawa and Miyako Island. It was the first time Chinese and Russian ships were spotted transiting that area together.

The ships have apparently taken part in a joint patrol China and Russia recently conducted in the Pacific Ocean.

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The Japanese Defense Ministry views the repeated joint military activities by the two countries around Japan as "clearly aimed at demonstrating their force against our country," according to officials.

The ministry also said it conveyed its concerns to China and Russia through diplomatic channels "from the viewpoint of national security."

According to the ministry, six Chinese ships, among them missile destroyers, and five Russian vessels, some being destroyers, were spotted 280 kilometers northeast of Japan's southernmost Okinotori Island in the Pacific on Tuesday morning.

Many of the same vessels were seen in July sailing through the Soya Strait between Hokkaido and Sakhalin to the Sea of Okhotsk after conducting joint drills in the Sea of Japan.

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