China has lodged a diplomatic protest after US President-elect Donald Trump spoke by phone with President Tsai Ing-wen of Taiwan but blames the self-ruled island Beijing claims as its own for the "petty" move.
The 10-minute telephone call with Taiwan's leadership was the first by a US president-elect or president since Jimmy Carter switched diplomatic recognition from Taiwan to China in 1979, acknowledging Taiwan as part of "one China".
China's Foreign Ministry said on Saturday it had lodged "stern representations" with what it called the "relevant US side", urging careful handling of the issue to avoid unnecessary disturbances in ties.
"The one China principle is the political basis of the China-US relationship," it said.
The wording implied the protest had gone to the Trump camp but the ministry provided no explanation.
Hours after Friday's phone call, Chinese Foreign Minister Wang Yi pointedly blamed Taiwan for the exchange, rather than Trump, a billionaire businessman with little foreign policy experience.
"This is just the Taiwan side engaging in a petty action and cannot change the 'one China' structure already formed by the international community," state media reported Mr Wang saying.
"I believe that it won't change the longstanding 'one China' policy of the United States government."
Mr Wang noted how quickly President Xi Jinping and Trump had spoken after Trump's victory and that Trump had praised China as a great country.
Mr Wang said that exchange had sent "a very positive signal about the future development of Sino-US relations", according to the Chinese Foreign Ministry's website. Taiwan was not mentioned in that call, according to an official Chinese transcript.
Mr Trump said on Twitter Tsai had initiated Saturday's call. "The President of Taiwan CALLED ME today to wish me congratulations on winning the Presidency. Thank you!" he said.
Alex Huang, a spokesman for Tsai, said: "Of course both sides agreed ahead of time before making contact."
Mr Trump and Mr Tsai noted that "close economic, political and security ties exist between Taiwan and the United States", the Trump transition team said in a statement. Taiwan's presidential office said the two discussed strengthening bilateral interactions and establishing closer co-operation.
China considers Taiwan a wayward province and has never renounced the use of force to bring it under its control.
Relations between the two sides have worsened since Mr Tsai, who heads the pro-independence Democratic Progressive Party, was elected president in January.
Chinese state media downplayed the possibility of a major blow-up in Beijing's relations with Washington as Mr Trump prepares to assume office.
Influential state-run tabloid the Global Times said in an online editorial if Mr Trump really overturned the "one China" principle upon assuming office it would create such a crisis with China he'd have little time to do anything else.
"We believe this is not something the shrewd Trump wants to do."