BEIJING, June 12 (Xinhua) -- A Foreign Ministry spokesperson has urged Japan not to weigh into territorial disputes in the South China Sea, labelling Japan a "non-party" in the matter.

Hong Lei made the comments at a media briefing on Friday responding to reporter's question on Japan's recent hyping up the South China Sea issue and Japanese Prime Minister Shinzo Abe more recently expressing "serious concern" over China's construction activities on islands and reefs of Nansha Islands in the South China Sea.

"China has voiced strong concern and indignation over Japan's negative moves, and has lodged solemn representations," Hong said.

"As a non-party to the South China Sea issue, Japan has been behaving very abnormally recently by deliberately interfering in the issue, stirring up dispute among regional countries and creating tension at sea."

He said China has indisputable sovereignty over the Nansha Islands and its surrounding waters. He said China's construction activities on some garrisoned islands and reefs of the Nansha Islands in the South China Sea is totally within its sovereignty. "They are lawful, reasonable and justified, which does not affect or target any other countries and beyond reproach".

"Japan's move neither contributes to resolving the South China Sea disputes nor protecting peace and stability in the South China Sea. It severely undermines security and political mutual trust between China and Japan and runs counter to improving bilateral ties," according to the spokesman.

Hong urged Japan to honor its commitment of not taking sides and respect the efforts of China and ASEAN countries to maintain peace in the South China Sea.