WASHINGTON (Reuters) - In a veiled warning to U.S. President-elect Donald Trump, China’s ambassador to the United States said on Wednesday that Beijing would never bargain with Washington over issues involving its national sovereignty or territorial integrity.

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Ambassador Cui Tiankai, speaking to executives of top U.S. companies, said China and the United States needed to work to strengthen their relationship.

“The political foundation of China-U.S. relations should not be undermined. It should be preserved,” Cui said.

“And basic norms of international relations should be observed, not ignored, certainly not be seen as something you can trade off,” he said. “And indeed, national sovereignty and territorial integrity are not bargaining chips. Absolutely not. I hope everybody would understand that.”

He did not specifically mention Taiwan, or Trump’s comments last weekend that the United States did not necessarily have to stick to its nearly four-decade policy of recognizing that Taiwan is part of “one China.”

Cui’s remarks were in line with recent protests from China’s Foreign Ministry, which regards the “one China” principle as the “political basis” for U.S.-China ties..

Beijing regards Taiwan as a renegade province and has never renounced the use of force to bring it under its control. China considers Taiwan independence a red line issue.

On Thursday, China’s influential state-run tabloid the Global Times said China needed to take the lead in deciding the island’s future.

“It is hoped that peace in the Taiwan Straits won’t be disrupted. But the Chinese mainland should display its resolution to recover Taiwan by force. Peace does not belong to cowards,” it said in an editorial.

Trump, in an interview on “Fox News Sunday,” suggested that the U.S. position on Taiwan could become part of his pledge to negotiate more favorable trade terms with China.

“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 said.

Trump’s comments came after he prompted a diplomatic protest from China over his decision to accept a telephone call from Taiwan’s president on Dec. 2.

U.S. corporate executives are increasingly pessimistic about their business prospects in China in light of tough restrictions on foreign investment in the country’s vast service sector, new cyber-security regulations that favor domestic technologies and weak enforcement of intellectual property protections.

Earlier on Wednesday, news that Chinese officials may penalize a U.S. automaker for monopolistic pricing behavior pushed down shares of General Motors Co GM.N and Ford Motor Co F.N.

Cui did not mention the autos case, but said: “China will ensure that there is a level playing field, for all companies, in China, both domestic and foreign.”