US President-elect Donald Trump has spoken directly with the president of Taiwan - breaking with US policy set in 1979 when formal relations were cut.
Mr Trump's transition team said he and Tsai Ing-wen noted "close economic, political, and security ties" between the US and Taiwan in a phone call.
Mr Trump then released a tweet saying Ms Tsai had called him.
The President of Taiwan CALLED ME today to wish me congratulations on winning the Presidency. Thank you!— Donald J. Trump (@realDonaldTrump) December 3, 2016
The move risks angering China, which sees Taiwan as a breakaway province.
China has hundreds of missiles pointing towards the island, and has threatened to take it by force if necessary.
A Hong Kong television station has reported China is blaming the Taiwanese president for the phone call, saying it was a "petty action" by the island's leadership.
It is reporting the Chinese Foreign Minister, Wang Yi, as saying the call will not change the US government's long-standing One China policy.
Mr Trump's team also said that the president-elect "congratulated" Ms Tsai on becoming the president of Taiwan in January's elections.
The 59-year-old, Taiwan's first female leader, led the Democratic Progressive Party (DPP) to a landslide victory in the poll.
The DPP has traditionally leaned towards independence from China.
Tsai Ing-wen, Taiwan's shy but steely leader
Washington cut formal diplomatic ties with Taiwan in 1979, expressing its support for Beijing's "One China" policy. China has offered a "one country, two systems" solution, like Hong Kong, to the dispute.
However, the US maintains friendly non-official relations with Taiwan.
- BBC / Reuters