"Diaoyu Island and the adjacent islands have been China's territory since ancient time. China has indisputable sovereignty over the islands," said Jiang Yu, a Chinese Foreign Ministry spokeswoman, at a regular press briefing.
Japanese officials said they filed a formal protest with Beijing after a Chinese ship defied warnings from Japan's coast guard and conducted a marine survey on Sunday.
Jiang did not comment directly on the complaint.
The island chain, called Diaoyu in Chinese and Senkaku in Japanese, is surrounded by rich fishing grounds and is regularly visited by nationalists from both sides.
Diplomats from Japan and China are to meet Saturday in Beijing for talks on disputed gas and oil deposits in the East China Sea. Earlier rounds of talks produced no major progress.
The giant neighbors have been feuding over undersea gas deposits and the delineation of their exclusive economic zones, the AP reports.
Also Tuesday, Chinese President Hu Jintao said he hoped China and Japan would make joint efforts to normalize ties, which are at their most strained in decades because of such disputes and visits by Japanese leaders to a Tokyo war shrine which honors Japan's war dead, including several convicted war criminals.
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