Representation. A file picture of Chinese naval vessels in East China Sea. China Daily/via 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.

The latest incident comes amid heightened tensions in Asia, 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 Coast Guard said. On Friday, a Japanese foreign ministry official said Chinese coastguard ships and fishing vessels 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 near 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 on Friday summoned China's ambassador to Japan, Cheng Yonghua, to lodge a strong protest, the ministry said.

Chinese officials could not immediately be reached for comment on Saturday.

China on Friday accused Japan's new defense minister, Tomomi Inada, of recklessly misrepresenting history after she declined to say whether Japanese troops 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 Japans' wartime occupation of parts of China and regional rivalry.