Japan went on high alert after several warships were spotted south of Tokyo. An increased presence of Russian and Chinese forces near the country’s territory raised concerns this week.

Seven Russian warships were seen moving southward off the coast of Japan’s northmost island, Hokkaido, on Thursday and Friday, according to the Japan Times. The vessels passed by the uninhabited Izu Islands.

Japan’s Joint Staff confirmed that the foreign vessels were monitored by ships and aircraft from the Maritime Self-Defense Force.

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The last time Russian warships were spotted near Japanese waters was in October. At that time, a total of 10 vessels from Russia and China were spotted making their way around the country.

On Friday, nine more nine more Russian vessels were spotted around Cape Soya, near the northernmost point of Hokkaido.

The warships were close to the Japanese waters but did not enter Tokyo’s territory. They also did not take any threatening or dangerous action. 

Russian forces had previously announced plans to run large-scale training drills in the Pacific Ocean with 40 warships. Japan’s Defense Ministry said that it was likely that the ships were taking part in those drills. However, there is no confirmation on the same so far.

The Joint Staff also announced that, around the same time, two Chinese missile destroyers were spotted passing through the seas of Japan, heading from the Tsushima Strait to the Okhotsk Sea.

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Tension between Japan and Russia escalated in April when Moscow warned of potential retaliation if Japanese and American vessels continued to run naval exercises near Russian waters.

There were reports that the U.S. Marine Corps was planning to run its largest-ever drills with Japan in September and October, known as “Resolute Dragon,” with more than 4,000 military members potentially taking place.

“We see such actions by the Japanese side as a threat to the security of our country,” Morgulov told the state-owned newswire RIA Novosti. “We directly warn Tokyo about this through diplomatic channels. They should be prepared for the fact that if such practices expand, Russia will take retaliatory measures in the interests of strengthening its defense capabilities.”