"The one-China principle is the consensus of the international community. It is also the political foundation on which China develops relations with other countries. It is a red line that must not be crossed," Chinese Vice Foreign Minister Ma Zhaoxu said in an interview with CGTN in Beijing on Tuesday, in response to U.S. House of Representatives Speaker Nancy Pelosi's recent visit to the Taiwan region.

"What does one China mean? There can only be one answer. That is, there is but one China in the world, Taiwan is part of China, and the government of the People's Republic of China is the sole legal government representing the whole of China," Ma reiterated.

This is a basic norm of international relations confirmed by UNGA Resolution 2758 and a commitment made by the U.S. in the three China.-U.S. joint communiqués, he stressed. "The principle, written down in black and white, is crystal clear. There is no room for ambiguity or arbitrary interpretation," he said.

The U.S. can only maintain cultural, commercial and other unofficial relations with Taiwan, according to the communiqués. The executive, legislative and judicial branches are all part of the U.S. government.

The U.S. has been undermining the one-China principle over the years, Ma said.

"Pelosi is the number three figure in the U.S. government. During her stay in Taiwan, she was speaking on behalf of the U.S. from the beginning to the end. Even she herself admits that it is an official visit. If this is not official engagement, then what is it?" Ma said.

The vice minister also pointed out that the U.S. has put into its so-called one-China policy some unilateral moves, including the "Taiwan Relations Act" and the "Six Assurances."

"This is against international law. China never accepts it, and is always opposed to it," he said.