US president-elect Donald Trump is unapologetic about the storm over his decision to speak on the phone with Taiwan's leader - a breach of long-standing tradition that risks enmity from China.
The US severed diplomatic ties with the self-governing island in 1979 but has maintained close unofficial relations and a commitment to support its defence.
Mr Trump's conversation with President Tsai Ing-wen drew an irritated, but understated response from China, with foreign minister Wang Yi saying the contact was "just a small trick by Taiwan" that he believed would not change US policy towards Beijing.
"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," Mr Wang said.
Chinese officials said they lodged a complaint with the US and reiterated a commitment to seeking "reunification" with the island, which they consider a renegade province.
After the phone conversation on Friday, Mr Trump tweeted that Ms Tsai "CALLED ME" and complained about the reaction to the call, saying: "Interesting how the US sells Taiwan billions of dollars of military equipment but I should not accept a congratulatory call."
America shifted diplomatic recognition to China from Taiwan in 1979. But the governments in Washington and Taipei have maintained close unofficial ties and deep economic and defence relations. The US is required by law to provide Taiwan with weapons to maintain its defence.
Since 2009 the Obama administration has approved 14 billion dollars (£11bn) in arms sales to Taiwan.
The call was the starkest example yet of how Mr Trump has flouted diplomatic conventions since he won the Novemnber 8 US election. He has apparently undertaken calls with foreign leaders without guidance customarily given by the State Department, which oversees the country's 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," said Bonnie Glaser, senior adviser for Asia at the Centre for Strategic and International Studies in Washington.
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 and would regard any recognition of a Taiwanese leader as a head of state as unacceptable.
Taiwanese newspapers ran banner headlines on Sunday about the call, with two noting on their front pages that Mr Trump referred to Ms Tsai as "the president of Taiwan" - a formulation that would be a huge shift in American policy and infuriate China.
But Douglas Paal, a former director of the American Institute in Taiwan, which unofficially represents US interests in Taipei, said it was too soon to judge whether Mr Trump was going to lead that shift, or if the incident was just a "complicated accident".
"Beijing will watch closely to see which it is," said Mr Paal, now vice president for studies at the Carnegie Endowment for International Peace. "But until someone from Trump Tower explains further, it is unknowable."
Yang Chih-kai, a 22-year-old university student in New Taipei City, said the call raised Taiwanese hopes for a stronger relationship with the United States, saying: "People will think that the US will keep on helping Taiwan protect itself against China's threat."
Taiwan split from the Chinese mainland in 1949. The US policy acknowledges the Chinese view over sovereignty, but considers Taiwan's status as unsettled.
Ned Price, a spokesman for the White House National Security Council, said Mr Trump's conversation did not signal any change to long-standing US policy on cross-strait issues.
The Taiwanese presidential office said Mr Trump and Ms 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 co-operative relations," a statement said.
Ms Tsai also told Mr Trump that she hoped the US would support Taiwan in its participation in international affairs, the office said, in an apparent reference to China's efforts to isolate Taiwan from global institutions such as the United Nations.
Taiwan's presidential office spokesman, Alex Huang, said separately that Taiwan's relations with China and "healthy" Taiwan-US bonds could proceed in parallel.
"There is no conflict" in that, he said.
China's foreign ministry said Beijing lodged "solemn representations" with the US over the call.
"It must be pointed out that there is only one China in the world and Taiwan is an inseparable part of Chinese territory," Geng Shuang, a ministry spokesman, said.
"The government of the People's Republic of China is the sole legitimate government representing China."
China is likely to be trying to identify whether this signals any intent on the part of Mr Trump to alter long-standing US policy towards Taiwan, Ms 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.