The US is pressing its ally Taiwan to explicitly state that a body set up to promote Chinese unification has not been abolished.
China has called Taiwan's President Chen a "troublemaker"
The US has been alarmed by Taiwanese President Chen Shui-bian's announcement this week that the National Unification Council had "ceased to function".
The US is worried that abolishing the body risks upsetting the delicate status quo between Taiwan and China.
China has already warned that Mr Chen's move "could bring disaster".
A statement released by the US Department of State on Thursday night called on Taiwan to "unambiguously affirm" that Mr Chen's announcement did not abolish the National Unification Council or change the status quo.
Taiwan has yet to respond to the call.
The attention being paid to the announcement's wording underlined how sensitive China-Taiwan relations have become, analysts said.
China and Taiwan have been governed separately since a civil war ended in 1949, but China still sees Taiwan as its territory and has threatened to use force if the island moves towards declaring independence.
China believes that Mr Chen, by measures such as scrapping the National Unification Council, is edging Taiwan towards formal independence.
The US, Taiwan's closest ally in the face of China's threat, has made clear that it supports the status quo.
Washington's call for Taiwan to clarify the council's status will be seen as a warning to Mr Chen not to challenge the status quo any further.
Taiwan complains that it is China who has changed the status quo, by building up its military offensive capability across the Taiwan Strait. Taiwan says China has at least 700 ballistic missiles targeting the island.
The National Unification Council was set up in 1990 as an attempt to convince the Chinese authorities that Taiwan was committed to reunification, and it helped kick-start landmark talks between the two sides in the early 1990s.