China’s foreign ministry says it has lodged a complaint with the US after Donald Trump spoke to Taiwan’s President Tsai Ing-wen in a phone call.

China sees Taiwan as a breakaway province. US policy set in 1979 cut all formal relations with Taiwan.

However, Donald Trump’s transition team said he and Tsai Ing-wen noted “close economic, political, and security ties” in a phone call.

China said it had lodged a “solemn representation” with Washington.

According to Chinese state news agency Xinhua, China urged the US “to cautiously, properly handle Taiwan issue to avoid unnecessary disturbance to Sino-US relations”.

Earlier, Chinese Foreign Minister Wang Yi dismissed the call as a “petty trick” by Taiwan, Chinese state media said.

Donald Trump tweeted on December 2 that Tsai Ing-wen had called Donald Trump to congratulate him on winning the US election.

His team said that the US president-elect had also congratulated Tsai Ing-wen on becoming the president of Taiwan last January.

It is highly unusual for a US president or president-elect to speak to a Taiwanese leader directly.

Following media reports pointing out the risks of angering China, Donald Trump tweeted: “Interesting how the US sells Taiwan billions of dollars of military equipment but I should not accept a congratulatory call.”

The White House has said Donald Trump’s conversation does not signal any change in US policy. And according to media reports, the White House learned of the call only after it had happened.

Donald Trump’s spokeswoman said he was “well aware” of US policy towards Taiwan.

The split between China and Taiwan goes back to 1949, when the Republic of China (ROC) government fled the mainland to Taiwan. After 1945, it held China’s seat on the UN Security Council and was, for a while, recognized by many Western nations as the only Chinese government.

In 1971, the UN switched diplomatic recognition to Beijing and the ROC government was forced out. Only a handful of countries now recognize Taiwan’s government.

The US cut formal diplomatic ties with Taiwan in 1979, expressing its support for Beijing’s “One China” concept, which states that Taiwan is part of China.

China has hundreds of missiles pointing towards Taiwan, and has threatened to use force if it seeks independence.

President Tsai Ing-wen, Taiwan’s first female leader, led the Democratic Progressive Party (DPP) to a landslide victory in the January 2016 election.

The DPP has traditionally leaned towards independence from China. President Tsai Ing-wen’s administration does not accept the One China policy.

The Chinese Ministry of Foreign Affairs said it opposed any official interaction or military contact between the US and Taiwan, according to the People’s Daily, a Communist Party mouthpiece.

Foreign Minister Wang Yi said the conversation between Donald Trump and Tsai Ing-wen was “just a petty trick by Taiwan” that he believed would not change US policy toward China, state media reported.

“The One China policy is the cornerstone of the healthy development of China-US relations and we hope this political foundation will not be interfered with or damaged,” he was quoted as saying.

The comment was repeated in a formal statement by the Foreign Ministry reported by Xinhua.

Despite the cut in formal ties nearly four decades ago, the US has still maintained friendly non-official relations with Taiwan.

Following Donald Trump’s phone call, the White House said the US remained firmly committed to its “One China” policy.