WASHINGTON/BEIJING – China expressed “serious concern” on Monday after U.S. President-elect Donald Trump said the United States did not necessarily have to stick to its long-held stance that Taiwan is part of “one China,” calling it the basis for relations.

Trump’s comments on “Fox News Sunday,” questioning nearly four decades of U.S. policy, came after he prompted a diplomatic protest from China over his decision to accept a phone call from Taiwan President Tsai Ing-wen on Dec. 2.

China’s Foreign Ministry said cooperation was “out of the question” if Washington could not recognise Beijing’s core interest on Taiwan, indicating it would reject any effort by Trump to use the issue as a bargaining chip in a long list of commercial and security problems facing the two countries.

“China has noted the report and expresses serious concern about it. I want to stress that the Taiwan issue concerns China’s sovereignty and territorial integrity, and involves China’s core interests,” said ministry spokesman Geng Shuang.

“Upholding the ‘one China’ principle is the political basis for developing China-U.S. ties. If this basis is interfered with or damaged then the healthy development of China-U.S. relations and bilateral cooperation in important areas is out of the question,” Geng told a daily news briefing.

“I fully understand the ‘one China’ policy, but I don’t know why we have to be bound by a ‘one China’ policy unless we make a deal with China having to do with other things, including trade,” Trump told Fox.

Trump’s call with Tsai was the first such contact with Taiwan by a U.S. president-elect or president since former President Jimmy Carter switched diplomatic recognition from Taiwan to China in 1979, acknowledging Taiwan as part of “one China.”

After Trump’s phone conversation with Tsai, the Obama administration said senior White House aides had spoken with Chinese officials to insist that Washington’s “one China” policy remains intact. The administration also warned that progress made in the U.S. relationship with China could be undermined by a “flaring up” of the Taiwan issue.

Geng said China’s top diplomat Yang Jiechi, who outranks the foreign minister, had met with Trump advisers, including his pick for national security adviser, retired Army Lt. Gen. Michael Flynn, during a transit in New York on his way to Latin America in recent days.

“Both sides exchanged views on China-U.S. ties and important issues both are concerned with,” Geng said, without elaborating.

He did not give a precise date for the meeting, and it was unclear if it occurred before or after Trump’s latest remarks on Taiwan, which Beijing considers a renegade province.

In the Fox interview, Trump criticized China over its currency policies, its activities in the South China Sea and its stance toward North Korea. He said it is not up to Beijing todecide whether he should take a call from Taiwan’s leader.

“I don’t want China dictating to me and this was a call put in to me,” Trump said. “It was a very nice call. Short. And why should some other nation be able to say I can’t take a call?”

“I think it actually would’ve been very disrespectful, to be honest with you, not taking it,” Trump added.

Trump plans to nominate a long-standing friend of Beijing, Iowa Gov. Terry Branstad, as the next U.S. ambassador to China. But Trump is considering John Bolton, a former Bush administration official who has urged a tougher line on Beijing, for a senior role at the U.S. State Department, according to a source familiar with the matter.

Some U.S. analysts warned that Trump could provoke a military confrontation if he presses the Taiwan issue too far.

“China is more likely to let the whole relationship with the United States deteriorate in order to show its resolve on the Taiwan issue,” said Jessica Chen Weiss, an associate professor of government at Cornell University and an expert in Chinese nationalism.

“When the decision to end a decades-long practice is made with so little warning and clear communication, it raises the likelihood of misunderstanding and miscalculation and sets the stage for a crisis between the United States and China over Taiwan,” Chen Weiss said.

In the same “Fox News Sunday” interview Trump also signalled a departure from long-standing policy on intelligence briefings, saying he was not interested in daily updates while dismissing a recent CIA assessment of Russian hacking as “ridiculous.”

“I get it when I need it,” he said of the top-secret briefings sessions, adding that he’s leaving it up to the briefers to decide when a development represents a “change” big enough to notify him.

“I’m, like, a smart person. I don’t have to be told the same thing in the same words every single day for the next eight years,” Trump said.

The CIA has concluded with “high confidence” that Russia sought to influence the U.S. election on behalf of Trump. The finding alarmed lawmakers, including Senate Armed Services Committee Chairman John McCain who said Sunday he planned to put Sen. Lindsay Graham, a staunch Trump critic, in charge of investigating the claim.

However, Trump also rejected the CIA’s conclusion on Russia and blamed “very embarrassed” Democrats for the public release of the assessment. The Washington Post first reported the CIA finding on Friday.

“It’s ridiculous,” Trump said of the CIA’s assessment.

He added, however, that he doesn’t necessarily oppose President Barack Obama’s order for a review of campaign-season hacking.

A U.S. intelligence official, speaking on condition of anonymity, harshly criticized Trump’s rejection of the assessment that Russian hacking was intended to boost the president-elect’s prospects in the Nov. 8 election.

“It’s concerning that intelligence on Russian actions related to the U.S. election is being dismissed out of hand as false or politically partisan,” said the U.S. intelligence official.

Russian officials, who have previously vehemently denied accusations of interference in the U.S. election, were quiet.

McCain was at a loss on Sunday to explain Trump’s repudiation of the Russian meddling. “I don’t know what to make of it because it’s clear the Russians interfered,” McCain said on CBS.

“Whether they intended to interfere to the degree that they were trying to elect a certain candidate, I think that’s a subject of investigation, but the facts are stubborn things.”