China is continuing to pressure neighbors with outsized territorial claims, this time sending Coast Guard ships close to disputed islands claimed by Japan over the weekend.

In the second such incident in less than a week, four Chinese Coast Guard vessels entered waters surrounding an island chain controlled by Japan and known as Senkaku in Japanese, but are known as Diaoyu in China.

A statement from China’s State Oceanic Administration only said the four Chinese coast guard vessels were “patrolling in Chinese waters off the Diaoyu Islands.”

Tokyo has regularly complained via diplomatic channels that China’s repeated incursions into waters it does not control are a constant source of tension in the region.

The island chain is located in waters believed to harbor vast undersea natural resources. China has claimed the resources but Japan controls the island chain.

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