BEIJING (AP) -- China said Monday that it had "serious concern" about President-elect Donald Trump's most recent comments about Taiwan, and warned that any changes to how America deals with the self-governing island could damage diplomatic ties between Washington and Beijing.
China's comments came a day after Trump said in a television interview that he didn't feel "bound by a one-China policy."
Geng Shuang, a spokesman for China's foreign ministry, said that established policy is the "political foundation" of any diplomatic relationship between China and the U.S., and that any damage to it could render cooperation "out of the question."
"We urge the new U.S. leader and government to fully understand the seriousness of the Taiwan issue, and to continue to stick to the one-China policy," Geng said.
Since recognizing the People's Republic of China in 1979, the U.S. has adhered to the one-China policy, recognizing Beijing as the capital of China and maintaining only unofficial relations with Taiwan. American law, however, requires the U.S. to ensure that Taiwan has the means to defend itself and to treat all threats to the island as matters of serious concern.
China split from Taiwan amid civil war in 1949 and continues to regard the island as a breakaway province to be reunified with the mainland, by force if necessary.
Geng's comments are the strongest public condemnation China has made of Trump's criticisms of current American policy toward Taiwan.
Beijing was already angered by Trump's Dec. 2 phone call with Taiwanese President Tsai Ing-wen, the first time an American president or president-elect has publicly spoken to a Taiwanese leader in nearly four decades. China considers any reference to a separate Taiwanese head of state to be a grave insult.
Trump followed the call with two tweets accusing China of manipulating its currency, unfairly taxing American imports and provoking tensions in the South China Sea.
Over the weekend, he told "Fox News Sunday" that he wouldn't feel "bound by a one-China policy unless we make a deal with China having to do with other things, including trade."
Trump said his call with Tsai was "very nice" and strictly meant to congratulate him on his winning the presidential election.
"Why should some other nation be able to say I can't take a call?" he said. "I think it actually would've been very disrespectful, to be honest with you, not taking it."
Hours after the interview aired, China's Communist Party-controlled Global Times published a Chinese-language editorial headlined: "Trump, please listen clearly: 'One China' cannot be traded."
"China needs to launch a resolute struggle with him," the editorial said. "Only after he's hit some obstacles and truly understands that China and the rest of the world are not to be bullied will he gain some perception."
"Many people might be surprised at how the new U.S. leader is truly a 'businessman' through-and-through," the paper said, referring to Trump's suggestion of using the one-China policy as a bargaining chip. "But in the field of diplomacy, he is as ignorant as a child."
The Global Times, which is published by the party mouthpiece People's Daily, often runs commentaries that target nationalistic sentiment with provocative language.
Chinese officials have been more restrained so far. They may be still trying to learn how to make their positions clear to Trump without feeding a vicious cycle of insults and heightened tensions, said Dali Yang, a political science professor at the University of Chicago.
However, Trump's suggestion that he could negotiate on Taiwan likely went too far for China, Yang said.
"He expected for China to bargain again for the one-China position, perhaps by giving up something on trade or something of that nature," Yang said. "This is actually the foundation of the U.S.-China relationship, rather than something to be bargained over."