Russian and Chinese warships held their first joint patrols in the Western part of the Pacific ocean on October 17-23, Russia’s defence ministry said in a statement on Saturday.

Moscow and Beijing, which staged naval cooperation drills in the Sea of Japan earlier in October, have cultivated closer military and diplomatic ties in recent years at a time when their relations with the West have soured.

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The naval manoeuvres have been closely watched by Japan which said earlier this week that a group of 10 vessels from China and Russia sailed through the Tsugaru Strait separating Japan’s main island and its northern island of Hokkaido.

“The group of ships passed through the Tsugaru Strait for the first time as part of the patrol,” Russia’s defence ministry said in the statement. The strait is regarded as international waters.

“The tasks of the patrols were the demonstration of the Russian and Chinese state flags, maintaining of peace and stability in the Asia-Pacific region, and guardianship of the subjects of maritime economic activities of the two countries,” the ministry added.