US Secretary of State Condoleezza Rice says Washington is strongly opposed to Taiwan's plan for a referendum on United Nations membership.
Ms Rice said a referendum would bring "no real benefits"
Ms Rice said applying to the UN in the name of "Taiwan" was a "provocative policy" - it raised tensions in the Taiwan Strait "unnecessarily".
Taiwan has failed to join the UN under its formal name, Republic of China.
Beijing regards Taiwan as its territory and has blocked its bid to regain a UN membership the island lost in 1971.
At an end-of-year news conference at the state department, Ms Rice said: "We think that Taiwan's referendum to apply to the United Nations under the name 'Taiwan' is a provocative policy.
Ruled by separate governments since end of Chinese civil war in 1949
China considers the island part of its territory
China has offered a "one country, two systems" solution, like Hong Kong
Most people in Taiwan support status quo
"It unnecessarily raises tensions in the Taiwan Strait, and it promises no real benefits for the people of Taiwan on the international stage."
Beijing has attacked the referendum, calling it a precursor to attempts to declare independence.
It has consistently threatened to use force if that happens.
China and Taiwan have been separately governed since 1949.
Taiwan held a UN seat until 1971, as the Republic of China, but that seat was then given to Beijing.
The referendum has been scheduled for 22 March 2008, when presidential elections are also set to take place.
Current President Chen Shui-bian said recently: "China and Taiwan are two separate states on either side of the Taiwan Strait."