In a break with decades-long diplomatic tradition, President-elect Donald Trump spoke directly with the president of Taiwan, a move that drew an irate response from China and looked set to cast uncertainty over US policy toward Asia.
It is perhaps unprecedented for a US president or president-elect to speak directly with a leader of Taiwan, a self-governing island with which the US broke diplomatic ties with in 1979.
In first comments apparently to downplay the significance of the call, Chinese foreign minister Wang Yi said today the contact between Taiwan's president and Trump was ''just a small trick by Taiwan'' that he believed would not change US policy toward China, according to Hong Kong's Phoenix TV.
"The one-China policy is the cornerstone of the healthy development of China-US relations and we hope this political foundation will not be interfered with or damaged,'' Wang was quoted as saying.
Washington has pursued a so-called "One China'' policy since 1979, when it shifted diplomatic recognition of China from the government in Taiwan to the communist government on the mainland. Under that policy, the US recognizes Beijing as representing China but retains unofficial ties with Taiwan.
A statement from Trump's transition team said he spoke Friday with Taiwanese President Tsai Ing-wen, who offered her congratulations.
"During the discussion, they noted the close economic, political, and security ties ... between Taiwan and the United States. President-elect Trump also congratulated President Tsai on becoming President of Taiwan earlier this year,'' the statement said.
Trump tweeted later: "The President of Taiwan CALLED ME today to wish me congratulations on winning the Presidency. Thank you!''
About an hour later, Trump groused about the reaction to the call. ''Interesting how the US sells Taiwan billions of dollars of military equipment but I should not accept a congratulatory call,'' he tweeted.
The Taiwanese presidential office issued a statement early today saying Trump and Tsai discussed issues affecting Asia and the future of US relations with Taiwan.
''The (Taiwanese) president is looking forward to strengthening bilateral interactions and contacts as well as setting up closer cooperative relations,'' the statement said.
"The president also told US President-elect Trump that she hopes the US will continue to support Taiwan's efforts in having more opportunities to participate in and contribute to international affairs in the future,'' Tsai's office said.
It said the two also ''shared ideas and concepts'' on "promoting domestic economic development and strengthening national defence'' to improve the lives of ordinary people.
The White House learned of the conversation after it had taken place, said a senior Obama administration official, who requested anonymity because of the sensitive diplomatic relations involved.
China's embassy in Washington, its foreign ministry in Beijing and Taiwan Affairs Office did not respond to requests for comment.
Friday's call is the starkest example yet of how Trump has flouted diplomatic conventions since he won the 8 November election. He has apparently undertaken calls with foreign leaders without guidance customarily lent by the State Department, which oversees US diplomacy.
"President-elect Trump is just shooting from the hip, trying to take phone calls of congratulatory messages from leaders around the world without consideration for the implications,'' Bonnie Glaser, senior adviser for Asia at the Center for Strategic and International Studies in Washington, DC, told the Associated Press.
Glaser said such a call was "completely unprecedented'' or at least has never been known publicly. Beijing is expected to respond with a reminder to Trump about commitments the US has made to China on Taiwan, she said.
China is also likely to be trying to identify whether this signals any intent on the part of Trump to alter longstanding US policy toward Taiwan, Glaser said.
"They will hope that this is a misstep but I think privately, they will definitely seek to educate this incoming president and ensure that he understands the sensitivity of Taiwan,'' she said.
In particular, China would want to highlight to the incoming administration the risks involved in any form of signal from the United States that it supports strengthening a relationship with Taiwan under a president that Beijing views as pro-independence, Glaser added.
Trump had just last month had a call with Chinese President Xi Jinping during which Trump's office described him as saying he believed the two would have ''one of the strongest relationships for both countries''.
Tsai was democratically elected in January and took office in May. The traditional independence-leaning policies of her party have strained relations with Beijing.
Over the decades, the status of Taiwan has been one of the most sensitive issues in US-China relations. China regards Taiwan as part of its territory to be retaken by force, if necessary, if it seeks independence. It would regard any recognition of a Taiwanese leader as a head of state as unacceptable.
Taiwan split from the Chinese mainland amid civil war in 1949. The US policy acknowledges the Chinese view over sovereignty, but considers Taiwan's status as unsettled.
Although the US does not have formal diplomatic ties with Taiwan, it has close unofficial ties. Taiwan's government has a representative office in Washington and other US cities. The US also has legal commitments to help Taiwan maintain the ability to defend itself.
Taiwan is separated from China by the 177-kilometre-wide Taiwan Strait. The island counts the US as its most important security partner and source of arms, but it is increasingly outgunned by China.
Ned Price, a spokesman for the White House National Security Council, said Trump's conversation does not signal any change to long-standing US policy on cross-strait issues.