China voiced opposition to Japan's latest move concerning the Diaoyu Islands on Tuesday, stressing that Japan's unilateral actions are "illegal" and "invalid."

The remarks came after Japanese Chief Cabinet Secretary Osamu Fujimura said Monday that Japan has registered one of the four islands near the Diaoyu Islands as a national asset.

"Any unilateral actions adopted by the Japanese side concerning the Diaoyu Islands and their affiliated isles are illegal and invalid, and can not change the fact that they are part of Chinese territory," Chinese Foreign Ministry spokesman Hong Lei said at a routine press briefing.

He reiterated that the Diaoyu Islands and other affiliated isles have been an inherent part of Chinese territory since ancient times, and China holds indisputable sovereignty over them.

"China will continue to take necessary measures to firmly safeguard sovereignty over the Diaoyu Islands and the affiliated isles," Hong said.