Foreign policy experts are criticizing President-elect Donald Trump after reports surfaced Friday that he had a phone conversation with the leader of Taiwan, Tsai Ing-wen.

AP/Matt Rourke - apimages.com

Trump tweeted Friday that "[t]he President of Taiwan CALLED ME today to wish me congratulations on winning the Presidency" in response to criticism of the call.

The Associated Press described the call as "highly unusual" and "probably unprecedented" in light of the fact that the U.S. ended its official diplomatic relationship with the self-governing island in 1979. The call is likely to anger Chinese officials, as China considers Taiwan part of its territory and does not recognize its independence.

"During the discussion, they noted the close economic, political, and security ties between Taiwan and the United States," the Trump transition team remarked in an official statement about the call. "President-elect Trump also congratulated President Tsai on becoming President of Taiwan earlier this year."

Trump's reference to Tsai as the president of Taiwan also represented a break from U.S. policy.

According to Ari Fleischer, who served as the White House press secretary under President George W. Bush, U.S. officials are encouraged to refer to the island's leader as the president on Taiwan due to the sensitivity of Chinese-Taiwanese relations.

In a follow up tweet, Trump again responded to critics by pointing out that the U.S. provides the island with military equipment.

The U.S. and Taiwan maintain an unofficial relationship, which involves a trade partnership. In 2015, the U.S. and Taiwan traded $67 billion worth of goods, according to the U.S. Office of the United States Trade Representative.

The Atlantic's David Graham commented on the "weirdness" of the U.S.-Taiwain relationship, pointing out that Trump's call violates "fragile but functional status quo." Simply put, everyone know the U.S. and Taiwan deal with each other, but nobody is supposed to talk about it.

In a statement released on China's state-run CCTV Friday, the government said "there is no immediate reaction from the Chinese government to this call," but that "[t]he Mainland says it firmly opposes official contact in any form between Washington and Taipei," according to CNN.