http://www.bbc.com/news/world-us-canada-38191711US 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.
The move risks angering China, which sees Taiwan as a breakaway province.
Chinese Foreign Minister Wang Yi has reportedly dismissed the call as a "petty trick" by Taiwan.
Mr Trump tweeted that Ms Tsai had called him to congratulate him on winning the US election.
His team said that the US president-elect had also congratulated Ms Tsai on becoming the president of Taiwan in January's elections.
It is highly unusual for a US president or president-elect to speak to a Taiwanese leader directly.
From concern to alarm and anger - Carrie Gracie, BBC China editor, Beijing
The president elect's decision to turn his back on four decades of US protocol on Taiwan and speak directly to a president of Taiwan will stun policymakers in Beijing.
Since his election last month, they have struggled to understand who is advising Donald Trump on Asia and what his China policy will look like.
This move will turn concern into alarm and anger.
Beijing sees Taiwan as a province and denying it any of the trappings of an independent state is one of the key priorities of Chinese foreign policy.
Read more from Carrie: The Trump phone call that will stun Beijing
Following media reports pointing out the risks of angering China, Mr Trump tweeted: "Interesting how the US sells Taiwan billions of dollars of military equipment but I should not accept a congratulatory call."
The White House has said Mr Trump's conversation did not signal any change in US policy.
Mr Trump's spokeswoman said he was "well aware" of what US policy has been on Taiwan.
Washington cut formal diplomatic ties with Taiwan in 1979, expressing its support for Beijing's "One China" concept, which states that Taiwan is part of China.
'Cornerstone of China-US relations'
China has hundreds of missiles pointing towards Taiwan, and has threatened to use force if it seeks independence.
Responding to news of the call, the Chinese Ministry of Foreign Affairs said it opposed any official interaction or military contact between the US and Taiwan, according to Communist Party mouthpiece the People's Daily.
Foreign Minister Wang Yi said the conversation between Mr Trump and Ms Tsai was "just a petty 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," he was quoted as saying.
President Tsai, 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 and President Tsai's administration does not accept One China policy.
Tsai Ing-wen, Taiwan's shy but steely leader
Image captionMs Tsai's presidency is expected to see a change in the relationship between Taipei and Beijing
Despite the formal ties being cut nearly four decades ago, the US has still maintained friendly non-official relations with Taiwan.
Following Mr Trump's telephone conversation, the White House said the US remained firmly committed to its "One China" policy.
"Our fundamental interest is in peaceful and stable cross-strait relations," said Ned Price, a spokesman for the White House National Security Council.
Meanwhile, Mr Trump is also reported to have invited President Rodrigo Duterte of the Philippines to the White House next year during a "very engaging, animated" phone conversation, according to one of Mr Duterte's aides.
But a statement issued by Trump's transition team made no mention of an invitation.
The Philippines leader has had disagreements with President Barack Obama and has in the past insulted him. Mr Obama cancelled a planned meeting with him in September.