China's state media on Sunday slammed Japan's move to name islands at the edge of its territorial waters claimed by Beijing as a "farce", saying they already had Chinese names.
Tokyo on Friday named 160 uninhabited islands in the East China Sea which include five in an archipelago known as Senkaku in Japan and Diaoyu in China over which the two nations have long been at loggerheads.
"Japan's naming farce can't change China's sovereignty over Diaoyu Islands," was the headline of a commentary in China's state-run news agency Xinhua.
"Japan may believe that giving names to those islets is a show of its sovereignty, but it has to be reminded that those islets have already got a Chinese name," it added.
China's foreign ministry, reacting after Tokyo's move, described the action as "illegal and invalid" and said it did not "change anything to the fact" that the islands belonged to China.
"China is resolutely opposed to Japan's actions infringing China's sovereign rights," spokesman Qin Gang said in a statement.
Beijing claims that the Mandarin name of the Diaoyu Islands first appeared in writings in the early 15th century, proving that China had discovered and named the islands then.
Tokyo and Beijing's bitter and longstanding battle over ownership of the East China Sea chain was exacerbated when Japan nationalised some of the archipelago nearly two years ago.
Since then, the waters have seen increasingly dangerous standoffs in the sea and air around the contested territory.