Beijing criticized the US over President Joe Biden's recent remark on Washington's readiness to help Taiwan in the case of a mainland Chinese "attack", Chinese Foreign Ministry Spokesperson Mao Ning said on Monday.

"China expresses strong dissatisfaction and strong protest, and has already made a representation to the US," Mao told reporters.

China will not tolerate any attempts to separate Taiwan and reserves the right to take appropriate measures, according to the diplomat, noting that Biden's remarks violate the One China principle, the three joint China-US communiqués, and the US commitment not to support Taiwan's independence.

China urges the US to recognize the significance and sensitivity of the Taiwan issue and not to underestimate Beijing's commitment to preserving its sovereignty, according to the Spokesperson.

Biden says US forces to defend Taiwan

Biden said US soldiers would defend Taiwan if China "intervened"; his most unequivocal remark on the matter to date, with statements aimed at enraging Beijing.

On CBS' 60 Minutes on Sunday, when asked whether the US military would protect the "democratically governed island claimed by China," he said, "Yes, if there was an unprecedented attack."

Biden again answered, "Yes," when asked if he meant that, unlike in Ukraine, US forces would protect Taiwan in the event of a Chinese "invasion".

The interview was simply the latest instance in which Biden appeared to go beyond long-standing official US policy on Taiwan, but his declaration about committing US troops to "defend" the island was clearer than prior ones.

US eyes on Taiwan 

Biden's words are expected to resonate across Beijing, which was already enraged by US House Speaker Nancy Pelosi's visit to Taiwan in August followed by other US officials' visits to the island. 

This visit prompted China to conduct its largest-ever military drills surrounding Taiwan, and China has condemned US senators' efforts to approve legislation that would strengthen US military assistance for Taiwan.

Xi warned Biden in a phone call in July not to play with fire over Taiwan, stating that "those who play with fire will perish by it."