Wang Zaixi, vice minister of the Taiwan Affairs Office, said China's Taiwan policy was based on the one-nation theory and any move in the other direction would invite war, the China Daily reported.

Wang was reacting to the aggressive stance taken by Taiwan's President, Chen Shui-bian, who has kicked off his campaign for next year's presidential elections with a pledge to amend the constitution.

"If the Taiwan authorities collude with all splittist forces to openly engage in pro-independence activities and challenge the mainland and the one-China principle, the use of force may become unavoidable," Wang said.
  
"(The separatist forces) are set to pay a high cost if they think we will not use force against their conspiracy to promote formal independence."

Beijing fears that a change in the constitution could speed up eventual Taiwan independence.
  
US steps in

The United States moved in quickly to ease the tension and urged both parties to show restraint.

"Our primary interests remain in maintaining stability in the Taiwan Strait," US embassy spokeswoman Sheila Paskman said.
  
"The US continues to urge Taiwan as well as the People's Republic of China to refrain from actions or statements that increase tensions or make dialogue more difficult to achieve.

"The US does not support Taiwan independence," Paskman added. 
  

Beijing firmly insists on its
one-China policy

Beijing also reacted sharply to comments made by Therese Shaheen, chairwoman of the American Institute in Taiwan (AIT), the de facto US embassy in Taiwan, when she denied that the US "opposes Taiwan independence".
  
"Shaheen, who was never present at any meetings between Chinese and US leaders, had no right to strike that attitude and openly deny that US leaders had said the United States opposes Taiwan independence," China's foreign ministry spokesman Liu Jianchao said.
  
"It's better for people like Shaheen to be aware of the sensitiveness of the Taiwan issue and the danger of Taiwan separatists, and behave discreetly to avoid being completely
ensnared by the Taiwan separatists."
  
Rhetoric aimed at US

Experts say China's rhetoric is aimed at the United States, especially following Chen's visit to the country earlier this month.
  
"These statements are a warning to the United States to stay out of the issue and not intefere in Taiwan elections," Kou Chien-Wen, an analyst at Taiwan's National Chengchi University, said.
  
He has added that Beijing's future stance will depend on how Premier Wen Jiabao's visit to Washington in December shapes up. 
  
China and Taiwan have been ruled separately since 1949, although Beijing considers the island part of its territory awaiting reunification, through force if necessary.