China has made serious demarches to Japan over its certain politician's visit to Taiwan and his irresponsible remarks, a Chinese Foreign Ministry spokesperson said on Tuesday.

Spokesperson Wang Wenbin made the remarks at a press briefing when asked to comment that according to a Japanese lawmaker who accompanied Taro Aso, Vice President of the Liberal Democratic Party and former Prime Minister of Japan, on his visit to Taiwan, Aso had discussed his remark in Taiwan about "a readiness to fight" and "deterrence" with the Japanese government beforehand, and the remark is in line with Japan's official view.

Taiwan is part of China, Wang said, pointing out that the Taiwan question is purely China's internal affair that brooks no foreign interference.

Wang pointed out that the Cairo Declaration issued by China, the U.S. and the UK in 1943 made it clear that Taiwan and all the other territories Japan stole from China shall be restored to China. Article 8 of the Potsdam Proclamation in 1945 reaffirms this. The Instrument of Surrender signed by Japan in 1945 says explicitly that Japan accepts the Potsdam Proclamation. The China-Japan Joint Statement signed in 1972 when the two sides normalized diplomatic relations states that the Japanese government fully understands and respects the position of the Chinese government that Taiwan is an inalienable part of China's territory and declares the commitment to Article 8 of the Potsdam Proclamation.

Wang said in 1978, the two countries concluded the Treaty of Peace and Friendship between China and Japan, which affirms the principles set out in the joint statement in legal form. The third and fourth political documents concluded in 1998 and 2008 respectively both reiterate Japan's commitment to the position on the Taiwan question stipulated in the joint statement. Japan has more than once made serious commitments to China on the Taiwan question, including not supporting "two Chinas," "one China, one Taiwan" or "Taiwan independence," and only maintaining people-to-people and region-to-region exchanges with Taiwan, Wang added.

"Those are the historical context of the issue, and the principles and position that Japan must abide by," said Wang.

"I wish to stress that the Taiwan question bears on China's core interests, the political foundation of China-Japan relations, and basic trust and principles between the two countries," Wang said, urging Japan to adhere to the one-China principle and the spirit of the four political documents between China and Japan, and take concrete action to honor its political commitment and related statements.

"China is ready to take all measures necessary to firmly safeguard its sovereignty and territorial integrity," Wang said.