In his first conversation with the Chinese leader since entering the Oval Office, Mr Trump said he would abide by the diplomatic formula that Beijing and Taipei agreed in 1992, the Financial Times reported ahead of the official White House release.
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Mr Trump had angered China in December by speaking to Tsai Ing-wen, the Taiwanese prime minister, in what was the first conservation between a U.S. president or president-elect and a Taiwanese leader since Washington and Beijing established diplomatic relations in 1979.
The phone call - on Thursday evening Washington time - came one day before Mr Trump will welcome Shinzo Abe, the Japanese prime minister, to the White House. The decision to speak to Mr Xi on the eve of the Trump-Abe summit was designed to reduce the fallout from the lavish welcome planned for the Japanese leader. Mr Abe will dine with Mr Trump four times, fly on Air Force One to the president's resort in Florida, and play golf with his U.S. counterpart.
Beijing will welcome Mr Trump's decision to back the "One China" policy, which has been the central principle governing relations between China and Taiwan, which the Chinese communist party regards as a renegade province.
Mr Trump also angered China in December by suggesting after his call with Ms Tsai that he would only support the "One China" policy if China agreed to do some kind of deal on trade with the US.