Beijing said it had lodged a protest with the United States over a visit by Washington’s environmental protection chief to Taiwan this week.
Environmental Protection Agency administrator Gina McCarthy’s visit is the first by a cabinet-level official since 2000, according to Taiwan’s presidential office. Taiwan President Ma Ying-jeou met her on Monday.
McCarthy was visiting to highlight environmental co-operation between the United States and partners in the Asia-Pacific region.
China’s foreign ministry said the visit to Taiwan, which the mainland considers a rebel province, violated promises made by Washington and that Beijing was "resolutely opposed" to it.
"No matter what goal the US EPA administrator has in visiting Taiwan, she has violated ... the promises made by the United States to China on the Taiwan issue," spokeswoman Hua Chunying told a daily news briefing.
"China expresses resolute opposition and strong dissatisfaction with this, and we have launched serious representations to the US side.
"We urge the US to prudently and appropriately deal with the issue in an effort to avoid doing further damage to the US-China relationship," Hua said.
The United States broke formal diplomatic ties with Taiwan in 1979 when it extended recognition to the government in Beijing, but maintains close unofficial relations with the democratic island.
The United States is also legally bound to come to Taiwan’s aid in the event of an attack, under the Taiwan Relations Act.
China's defence ministry earlier this month expressed anger after the US House of Representatives agreed to authorise the sale to Taiwan of four second-hand US warships, saying the United States had ignored Beijing's protests.