China on Thursday voiced strong dissatisfaction and lodged a stern representation to Japan over Prime Minister Taro Aso's remarks that the Diaoyu Islands are Japanese territory.

Local visitors look at the damage done to a Hong Kong boat used by activists to sail to the Diaoyu islands, October 30 2006, as they were given a heroes' welcome after a week-long voyage to the islands. [Agencies]

The Diaoyu Islands and adjacent islets had been Chinese territories since ancient times, Chinese Foreign Ministry spokesman Ma Zhaoxu said in a press release. China held "indisputable" sovereignty over the islands.

"Any word and deed by Japan attempting to change the fact are futile, and China stands firmly opposed to it," he said.

China and Japan disputed sovereignty of the Diaoyu Islands, and China has consistently advocated that the issue should be properly resolved through negotiation, said Ma.

He urged Japan to realize the great sensitivity of the Diaoyu Islands issue and proceed according to the general interests of China-Japan relations and regional stability, with discretion in word and deed.

In response to a question by the Democratic Party of Japan (DPJ)Thursday morning on countermeasures should the islands be encroached upon by a third country, Aso said they were Japanese territory and the Treaty of Mutual Cooperation and Security between Japan and United States would certainly apply to them.