(AP) -- President-elect Donald Trump spoke Friday with the president of Taiwan, a move that will be sure to anger China.

It is highly unusual, probably unprecedented, for a U.S. president or president-elect to speak directly with a leader of Taiwan, a self-governing island the U.S. broke diplomatic ties with in 1979.

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 U.S. recognizes Beijing as representing China but retains unofficial ties with Taiwan.

A statement from Trump's transition team said he spoke 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 U.S. 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 Saturday saying Trump and Tsai discussed issues affecting Asia and the future of U.S. 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 U.S. President-elect Trump that she hopes the U.S. 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 defense" 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 Nov. 8 election. He has apparently undertaken calls with foreign leaders without guidance customarily lent by the State Department, which oversees U.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 Center for Strategic and International Studies in Washington, D.C.

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 U.S. 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 U.S. 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 U.S.-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 U.S. policy acknowledges the Chinese view over sovereignty, but considers Taiwan's status as unsettled.

Although the U.S. does not have formal diplomatic ties with Taiwan, it has close unofficial ties. Taiwan's government has a representative office in Washington and other U.S. cities. The U.S. also has legal commitments to help Taiwan maintain the ability to defend itself.

Taiwan is separated from China by the 110-mile (177-kilometer)-wide Taiwan Strait. The island counts the U.S. 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 U.S. policy on cross-strait issues.

"We remain firmly committed to our 'one China' policy," Price said. "Our fundamental interest is in peaceful and stable cross-strait relations."

The NSC stressed that every president has benefited from the "expertise and counsel" of the State Department on matters like this, which suggested that the White House was frustrated by Trump's conversation with the Taiwanese leader.

Still, the White House said Obama remains committed to a smooth transition to the new administration.

Diplomatic protocol dictates that Taiwanese presidents can transit through the U.S. but not visit Washington.

Douglas Paal, who served as head of the American Institute in Taiwan during the George W. Bush administration, said that to his knowledge the call was unprecedented. He said he expected Beijing to issue a verbal warning that there's no space to change the rules over Taiwan relations.

In Beijing, a U.S. business group said it expected the new U.S. administration to respect the status quo.

"American business operating in Asia needs certainty and stability," said James Zimmerman, chairman of the American Chamber of Commerce in China. "The new administration needs to get up to speed quickly on the historical tensions and complex dynamics of the region."

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Wong reported from Beijing. Associated Press writers Jonathan Lemire in New York and Matthew Pennington and Darlene Superville in Washington contributed to this report.