President-elect Donald Trump has strayed from decades-long diplomatic tradition by speaking with Taiwan's leader Tsai Ing-wen.
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 US recognises Beijing as representing China, but retains unofficial ties with Taiwan.
Trump's transition team said of the conversation: "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 Taiwanese presidential office said the leaders discussed issues affecting Asia and the future of US relations with Taiwan.
"The (Taiwanese) president is looking forward to strengthening bilateral interactions and contacts as well as setting up closer co-operative relations," it said.
"The president also told US President-elect Trump that she hopes the US will continue to support Taiwan's efforts in having more opportunities to participate in and contribute to international affairs in the future."
It added that the two also "shared ideas and concepts" on "promoting domestic economic development and strengthening national defence" to improve the lives of ordinary people.
China's foreign minister Wang Yi has said he hopes Beijing's relations with the US would not be "interfered or damaged" by Trump's decision. Yi dismissed the call as "just a small trick by Taiwan", which he believed would not change US policy towards China, according to Hong Kong's Phoenix TV.
The White House learned of the conversation after it had taken place, said a senior Obama administration official.
Friday's call is the starkest example yet of how Trump has flouted diplomatic conventions since he won the November 8 election. He has apparently undertaken calls with foreign leaders without guidance customarily lent by the State Department, which oversees US diplomacy.
Ned Price, a spokesman for the White House National Security Council, said Trump's conversation did not signal any change to long-standing US 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."