BEIJING -- The Japanese government's move to "purchase" the Diaoyu Islands will inevitably have a negative impact on the Sino-Japan economic and trade ties, China's Vice-Minister of Commerce Jiang Zengwei said Thursday.

The Japanese government announced on Sept 10 the "purchase" of the Diaoyu Island and its affiliated Nan Xiaodao and Bei Xiaodao and the implementation of the so-called "nationalization" of the islands.

Jiang said the Diaoyu Island and its affiliated islands have been China's territory since ancient times and China has indisputable sovereignty over them.

The Japanese government's so-called "purchase" of the Diaoyu Islands is totally illegal and invalid and China firmly opposes it, Jiang said.

The two countries' trade cooperation requires joint efforts to make it mutually beneficial. Japan's so-called "purchase" of the Diaoyu Islands will "inevitably" have a negative impact on China-Japan economic and trade ties, Jiang said.

"If Chinese consumers, in a reasonable manner, express their positions and views against Japan's violation of China's territorial sovereignty, I think it is within their rights to do so and it is understandable," Jiang said.

Jiang said China-Japan economic and trade cooperation requires good political environment. "Good political environment and bilateral ties are foundation to bilateral as well as multilateral economic and trade relations."

China is Japan's biggest trading partner. Statistics from Japanese customs authorities showed Japan's exports to China amounted to $73.54 billion in the first half of the year, while imports from China totalled $91.29 billion during the period.