The Chinese government has said it is "seriously concerned" about Donald Trump's threat to change the US's stance on the recognition of Taiwan as an independent state.
The President-elect has suggested he could withdraw American support for the so-called "One China" principle unless Beijing makes concessions on other issues like trade.
The principle dictates that self-governing Taiwan is a part of China, and demands that any ally of Beijing has no official relations with Taipei.
China's foreign ministry said cooperation was “out of the question” if Washington could not recognise Beijing's core interest on Taiwan, indicating it would reject any effort by Mr Trump to use the issue as a bargaining chip in a long list of commercial and security problems facing the two countries.
“China has noted the report and expresses serious concern about it. I want to stress that the Taiwan issue concerns China's sovereignty and territorial integrity, and involves China's core interests,” said ministry spokesman Geng Shuang.
“Upholding the 'one China' principle is the political basis for developing China-US ties. If this basis is interfered with or damaged then the healthy development of China-US relations and bilateral cooperation in important areas is out of the question,” Mr Geng said.
It comes after a TV interview on Sunday in which Mr Trump said 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".
The status of Taiwan is the most sensitive issue in US-China relations, and Mr Trump sparked the diplomatic row when he accept an official phone call from the Taiwanese President Tsai Ing-wen. It was the first time an American president or president-elect has publicly spoken to a Taiwanese leader in nearly four decades.
The foreign ministry cited foreign minister Wang Yi as warning during a trip to Switzerland against moves to damage the “one China” principle, having been asked by a reporter about Mr Trump's call with Ms Tsai.
“China is paying close attention to developments,” Mr Wang said. “I can clearly say that no matter whether the Tsai Ing-wen authority, any other person in the world, or any other force, if they try and damage the one China principle and harm China's core interests, in the end they are lifting a rock only to drop it on their feet.”
Despite China's discontent, it has reached out to Mr Trump. Spokesman Mr Geng said China's top diplomat Yang Jiechi, who outranks the foreign minister, had met with Trump advisers, including his pick for national security adviser, retired Army Lieutenant General Michael Flynn, during a transit in New York on his way to Latin America in recent days.
“Both sides exchanged views on China-US ties and important issues both are concerned with,” Mr Geng said, without elaborating.
He did not give a precise date for the meeting, and it was unclear if it occurred before or after Trump's latest remarks on Taiwan, which Beijing considers a renegade province.
Some reports have questioned whether Mr Trump was aware of the significance of the call with Ms Tsai, and he has admitted he was informed only "an hour or two before".
But on Sunday, Mr Trump defended the decision. "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."
Earlier on Monday, an official Chinese newspaper called Mr Trump "as ignorant as a child" over his stance on Taiwan.
Hours after Mr Trump's interview with Fox News aired, the Global Times published a Chinese-language editorial headlined: "Trump, please listen clearly: 'One China' cannot be traded."
It read: "China needs to launch a resolute struggle with him. 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."
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