China condemns the Taiwan leader's so-called "stopover" in the U.S. and urged the U.S. side not to cross the "first red line" of the Taiwan question, Chinese Foreign Ministry spokesperson Mao Ning said at a press briefing in Beijing on Thursday.

The Taiwan question is the core of the core interests of China, the bedrock of the political foundation of China-U.S. relations, and the first red line that must not be crossed in China-U.S. relations, Mao said.