China has expressed "serious concern" about US president-elect Donald Trump's most recent comments concerning 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 Mr Trump said in a television interview that he did not 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 US, and that any damage to it could render co-operation between both sides to be "out of the question".
"We urge the new US leader and government to fully understand the seriousness of the Taiwan issue, and to continue to stick to the one-China policy," Mr Geng said.
Since recognising the People's Republic of China in 1979, the US has adhered to the one-China policy, recognising Beijing as the capital of China and maintaining only unofficial relations with Taiwan.
US law, however, requires America to ensure 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.
Mr Geng's comments are the strongest public condemnation China has made of Mr Trump's criticisms of current American policy towards Taiwan.
Beijing was already angered by Mr Trump's December 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.
Mr 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.
On Sunday, he told Fox News Sunday that he would not feel "bound by a one-China policy unless we make a deal with China having to do with other things, including trade".
Mr Trump said his call with Mr 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 US leader is truly a 'businessman' through and through," the paper said, referring to Mr 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 Communist Party's mouthpiece, the People's Daily, often runs commentaries that target nationalistic sentiment with provocative language.
Meanwhile a federal judge has rejected a Green Party-backed request to recount paper ballots in Pennsylvania's presidential election, won by Mr Trump, and scan some counties' election systems for signs of hacking.
The rejection by US District Judge Paul Diamond on Monday is the latest roadblock to a Pennsylvania recount.
It is part of a broader effort by Green Party presidential candidate Jill Stein to recount votes in Michigan, Pennsylvania and Wisconsin.
Mr Trump won all three states narrowly over Democrat Hillary Clinton.
President-elect Trump beat Ms Clinton in Pennsylvania by about 44,000 votes out of six million cast.
A federal judge halted Michigan's recount.
The Wisconsin recount was expected to conclude later on Monday. With about 95% of the votes recounted, Ms Clinton had gained 25 votes on Mr Trump, but still trailed by about 22,000.
