Japan's coast guard on Sunday warned a Chinese marine research ship sailing near a disputed island chain against conducting surveys there.
The ship, named the Beidou, was spotted early Sunday by a coast guard plane some 60 kilometers off Uotsuri, part the islands known as Senkaku by Japan and Diaoyu in Chinese, the Japan coast guard said.
The chain, rich in undersea natural resources, is also claimed by Taiwan.
It is the first time this year that a Chinese research vessel has been confirmed as having deployed near the Senkaku Islands, the coast guard said.
The plane and a coast guard patrol ship issued a warning for the ship not to conduct marine research in Japan's exclusive economic zone without its approval.
But the Chinese ship continued sailing without responding, trailing four wire-like objects from its stern, the coastguard said.
On July 4, Beijing lodged a formal complaint with Tokyo about Japanese fishing boats plying waters off the island chain in the East China Sea.
Beijing and Tokyo have repeatedly quarrelled over disputed maritime territories, and Japan has often voiced concern about China's rising defence spending and increasingly assertive stance as a naval power.
Last year, China and Japan locked horns over the same islands after Japan arrested a Chinese captain for ramming his trawler against Japanese coast guard ships in the area.© 2011 AFP