MOSCOW—Russian and Chinese warships held their first joint patrols in the western Pacific Ocean over the past week, Russia’s defense ministry said on Saturday, a move Japan said it was monitoring. 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. The naval maneuvers, which Russia said ran from Sunday through Saturday, have been closely watched by Japan, which said earlier in the 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 defense ministry said in a statement. The strait is regarded as international waters. “The tasks …