China says it has “serious concern” about President-elect Donald Trump’s latest comments suggesting he is reconsidering America’s relationship with Taiwan.

Geng Shuang, a spokesman for the Chinese foreign ministry, said Monday that Trump’s comments in a television interview over the weekend raised the possibility that U.S.-China relations would be “badly affected.” Geng said the “one China” policy was the “political foundation” of any Sino-American ties.

The United States switched relations from Taipei to Beijing in 1979. China considers Taiwan to be part of China and any reference to a separate Taiwanese government as a grave insult.

But Trump said on “Fox News Sunday” that he doesn’t feel “bound by a one-China policy unless we make a deal with China having to do with other things, including trade.”