President-elect Donald Trump spoke Friday with Taiwan's president, a major departure from decades of U.S. policy in Asia and a breach of diplomatic protocol with ramifications for the incoming president's relations with China.

The call is the first known contact between a U.S. president or president-elect with a Taiwanese leader since before the United States broke diplomatic relations with the island in 1979. China considers Taiwan a province, and news of the official outreach by Trump is likely to infuriate the regional military and economic power.

The exchange is one of a string of unorthodox conversations with foreign leaders that Trump has held since his election. It comes at a particularly tense time between China and Taiwan, which earlier this year elected a president, Tsai Ing-wen, who has refused to accept the notion of a unified China under Beijing's rule. Her election angered Beijing to the point of cutting off all official communication with the island government.

It is not clear whether Trump intends a more formal shift in U.S. relations with Taiwan or China. On the call, Trump and Tsai congratulated each other on winning election, a statement from Trump's transition office said.

"During the discussion, they noted the close economic, political, and security ties . . . between Taiwan and the United States," a statement from Trump's transition office said.

A spokeswoman for Taiwan in the United States said she could not immediately confirm that the conversation took place and said she was seeking guidance from Taiwan. The conversation was first reported by the Financial Times and the Taipei Times.

The president elect tweeted out Friday evening, "The president of Taiwan CALLED ME today to wish me congratulations on winning the Presidency."

The United States has pursued what it calls a "One China" policy since 1972, when then-President Richard M. Nixon visited China. In 1978, President Jimmy Carter recognized Beijing as the only government of both mainland China and Taiwan, and Washington closed its embassy in Taiwan a year later.

China guards the structures of its formal relationship with the United States very carefully - especially the founding document that established the One China policy. U.S. officials typically tiptoe around any mention of Taiwan or the Chinese goal of full reunification.

"This phone call calls into question whether or not Trump adheres to the basic foundation of the U.S.-China relationship," said Evan Medeiros, a former top China adviser to President Obama who is now an adviser at the Eurasia Group. "This action guarantees that U.S.-China relations under Trump will get off to a very rocky start."

Trump's growing team of national-security and foreign-policy advisers includes several people who have been strong supporters of Taiwan in Republican administrations. They include Stephen Yates, deputy national security adviser under Vice President Richard Cheney, who was reported to be visiting Taiwan when the call occurred.

Trump apparently considered hotel investments in Taiwan earlier this year. The mayor of Taoyuan said last month that a representative from the Trump Organization had visited and was interested in constructing hotels in the northwestern Taiwanese city, according to China Times. Trump has said he will separate himself from his businesses before he is inaugurated.

In recent years, in the face of Taiwan's waning economic power and decreasing international recognition as a separate entity from mainland China, Taiwanese diplomatic representatives in Washington have been trying to raise their stature. They have courted government officials and journalists with Taiwanese film screenings, expensive soirees and other cultural events around town.