Beijing has lodged a strong protest to the United States over a planned visit by Taiwan's deputy leader Lai Ching-te, urging Washington to avoid crossing the nation's "red line".

Foreign Ministry spokeswoman Mao Ning said on Monday that China is firmly opposed to any form of official exchange between the US and Taiwan, as well as any US visit made by "Taiwan independence" separatists under any pretext.

China is also firmly against the US supporting "Taiwan independence" separatists and their actions in any way, Mao added.

It has been reported that Lai will make stopovers in the US on his way to and from Paraguay next month.

"The Taiwan question is at the very core of China's core interests, as well as the first red line in China-US relations that must not be crossed," Mao said.

The spokeswoman urged the US to observe the one-China principle and the stipulations in the three China-US joint communiques, and deliver on US President Joe Biden's commitment to not support "Taiwan independence".

The US must also halt any official interactions with Taiwan authorities, stop upgrading its substantive exchanges with the region and cease sending erroneous signals to "Taiwan independence" separatists, the spokeswoman said.

"China will closely follow the development of the situation, and take resolute and forceful measures to safeguard its national sovereignty and territorial integrity," Mao said.

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