China accused the US of tampering with its political promises on Taiwan, days after a high-level meeting brought hope of stabilizing ties, showing the limits to resolving fundamental differences between the world’s two largest economies.

Yang Tao, a foreign ministry official, reiterated criticisms of the US for allegedly distorting its one China policy at a media briefing hours after Chinese President Xi Jinping met with visiting US Secretary of State Antony Blinken in Beijing, according to a readout the ministry published on its website on Wednesday.

“The US has made a clear promise, recognizing there is only one China in the world, Taiwan is a part of China, and that the People’s Republic of China is the only legitimate government representing China,” Yang said.

Yang suggested that policy has been undercut by the US decision to append the Taiwan Relations Act and the so-called Six Assurances to Taiwan to its one China policy over the years, saying they conflicted with what Beijing and Washington mutually agreed. “China has resolutely opposed them and does not recognize them,” he added.

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During Blinken’s visit to Beijing, China’s top diplomat, Wang Yi, and foreign minister Qin Gang both reiterated that Taiwan is the “core of the core interests of China,” and the self-governing island has been at the center of tensions between the two nations.

While Yang’s complaints aren’t new, they could be an effort to reiterate continuing frustrations Beijing has with Washington for domestic political purposes.

Recently, China has been alarmed by President Joe Biden’s repeated statements that the US would defend Taiwan if attacked, appearing to go beyond a strategy of being deliberately vague about how Washington would respond. While Biden’s aides say US policy hasn’t changed, the president’s comments suggest it has.

The US has for decades said its policy toward Taiwan is “guided” by the three joint communiques negotiated with Beijing as well as the 1979 Taiwan Relations Act and the Six Assurances, which Washington agreed to with Taipei in 1982 while negotiating the third communique with China. Beijing doesn’t endorse those separate agreements, which touch on arms sales to Taiwan as well as ruling out the US as a mediator between Taipei and Beijing, among other things.

America’s one China policy dates back to the 1970s when then-President Richard Nixon sought to establish ties with Beijing. In it, Washington recognized the People’s Republic as the “sole legal government of China,” without clarifying its position on Taiwan’s sovereignty.