A Foreign Ministry spokesman said Tuesday that any private deals made between the United States and Japan after the World War II concerning the Diaoyu Islands are illegal and invalid.

Spokesman Liu Weimin made the remark at a regular press briefing when asked to comment on a recent U.S. claim that the Diaoyu Islands and their affiliated islands fall within the scope of a 1960 U.S.-Japan security treaty.

"China has expressed grave concern and firmly opposes such a claim," Liu said. "The Diaoyu Islands and their affiliated islands have been China's inherent territory since ancient times and China has indisputable sovereignty over them."

According to Japan's Kyodo News Agency, a senior U.S. State Department official said Monday that the Diaoyu Islands (referred to as the Senkaku Islands in Japan) fall within the scope of Article 5 of the U.S.-Japan Treaty of Mutual Cooperation and Security, as the Senkaku Islands have been under the administrative control of the government of Japan since they were returned as part of the reversion of Okinawa in 1972.

"Private deals made between the U.S. and Japan after World War II concerning the Diaoyu Islands are illegal and invalid," Liu said.

The U.S.-Japan Security Treaty should not undermine the interests of third parties, including China, Liu said.

"We hope concerned countries can contribute more to regional peace and stability," Liu added.