TOKYO (Reuters) - Japan issued a new protest to Beijing on Saturday after Chinese coastguard ships and about 230 fishing vessels sailed close to what Tokyo considers its territorial waters around disputed islets in the East China Sea, Japan’s foreign ministry said.

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The latest incident comes amid heightened tensions, less than a month after an arbitration court in The Hague invalidated China’s sweeping claims in the disputed South China Sea, in a case brought by the Philippines.

China has refused to recognize the ruling. Japan called on China to adhere to the verdict, which it said was binding, prompting warnings from Beijing to Tokyo not to interfere.

Three of the six Chinese coastguard ships that were in the so-called contiguous waters on Saturday appeared to be armed, Japan’s coastguard said.

On Friday, a Japanese foreign ministry official said Chinese coastguard ships and fishing vessels had entered what Tokyo considers its territorial waters around the islets.

Beijing claims the uninhabited, Tokyo-controlled East China Sea islands, called the Senkaku in Japan and Diaoyu in China, and occasionally sends its coastguard vessels close to them.

A senior Japanese foreign ministry official on Saturday issued a protest to a Chinese embassy official in Tokyo, calling on the coastguard ships to leave the area immediately and condemning the action as a unilateral escalation of tensions, the ministry said.

Japanese Vice Foreign Minister Shinsuke Sugiyama had on Friday summoned China’s ambassador to Japan, Cheng Yonghua, to lodge a strong protest, the ministry said.

China’s foreign ministry spokeswoman Hua Chunying, in a statement posted on the ministry’s website, said China had indisputable sovereignty over the islands and nearby waters.

“At the same time, China is adopting measures to appropriately manage the situation in relevant waters,” Hua said.

Japan should make “constructive efforts for stability” and not take actions that might complicate the situation, she said, without elaborating.

China on Friday accused Japan’s new defense minister, Tomomi Inada, of recklessly misrepresenting history after she declined to say whether Japanese troops had massacred civilians in China during World War Two.

Ties between China and Japan, the world’s second and third largest economies, have been plagued by the territorial row, the legacy of Japan’s wartime occupation of parts of China and regional rivalry.