The Taiwan question is at the core of China's core interests and concerns the political foundation of China-Japan relations, making it a red line that cannot be crossed, Chinese Foreign Ministry spokesperson Lin Jian said on Wednesday.

There is only one China, and Taiwan is an inseparable part of China's territory, Lin said at a press conference.

China firmly opposes any form of official interaction between countries with which China has diplomatic relations and Taiwan, and has lodged a stern protest with Japan on this matter, according to the spokesperson.

Japan ruled Taiwan as a colony for half a century, committing countless crimes and bearing serious historical responsibilities toward the Chinese people, Lin said. 

Certain Japanese politicians should remember the lessons of history, recognize the fact that there is only one China and that Taiwan is a part of China, and adhere to the one-China principle and the spirit of the four political documents between China and Japan, he said.

They should stop sending the wrong signals to the "Taiwan independence" separatist forces, Lin said, adding that the Democratic Progressive Party (DPP) authorities in Taiwan, who stubbornly uphold the separatist stance of "Taiwan independence" and collude with external forces to seek independence by relying on foreign powers, are doomed to fail.