Earlier China warned of "unbearable consequences" if US House Speaker visits self-governed island
A plane carrying Nancy Pelosi has landed in Taiwan.
Beijing, which considers Taiwan an integral part of its territory under the One China policy, has been vigorously protesting the possible trip, threatening the US with "unbearable consequences" if it happens.
Taiwan wasn't mentioned among the official destinations of the speaker's Asian tour, which included Singapore, Malaysia, South Korea and Japan, but media reports claimed that she could still visit the island.
China conducted live-fire military drills on Saturday off the coast of the southeastern province of Fujian, just across the strait between the mainland and Taiwan, in the wake of Pelosi's trip to the region.
Despite agreeing with the One China policy on paper, the US maintains strong unofficial ties with the island of 23.5 million, selling weapons to Taipei and backing its push for sovereignty. Taiwan has been self-governed since 1949, but never officially declared independence from Beijing.
On Monday, China's ambassador to the UN, Zhang Jun, reiterated that the One China principle is "a red line" in Beijing's relations with other nations, and no one will be allowed to cross it.
"China is fully prepared to respond. If the US insists on making the visit, China will take firm and strong measures to safeguard its national sovereignty and territorial integrity, and the US has to bear all the serious consequences arising thereof," Zhang warned.