A Foreign Ministry spokesman said Monday that China has lodged a solemn representation to Japan over a survey conducted by the Tokyo government in waters near the Diaoyu Islands.

"Any unilateral action by Japan regarding the Diaoyu Islands is illegal and invalid," spokesman Hong Lei said at a routine press briefing.

Media reports stated that a survey group organized by the Tokyo government arrived in waters near Diaoyu Islands in the East China Sea to conduct a survey around the islands Sunday morning.

Hong stressed that the Diaoyu Islands have been China's inherent territory since ancient times, adding that China holds indisputable sovereignty over the islands.

Tokyo Governor Shintaro Ishihara provoked the Chinese government in April by claiming to purchase the islands.

Hong said any action by the Japanese side to "nationalize" the islands will be in vain.

Regarding the U.S. position that the Diaoyu Islands fall under the scope of a 1960 Japan-U.S. security treaty, Hong said the treaty is a relic of the Cold War, adding that the treaty should not extend beyond Japan and the U.S. or hurt third-party interests.

"We hope the U.S. side will refrain from taking a position on the issue in order to maintain regional stability," Hong said.

"The turbulence occurring in China-Japan relations has mainly been caused by illegal activity by Japan that has infringed on China's sovereignty over the Diaoyu Islands," Hong said, adding the moves are futile and cannot change China's resolve to safeguard its sovereignty.

China hopes Japan will refrain from any activity that undermines China's territorial integrity, return to conducting dialogues and safeguard the overall condition of bilateral ties, Hong said.