Taiwan's independence movement is facing its biggest challenge yet following the recent US shift in cross-strait policy towards the mainland, a top political analyst from the island said yesterday. Philip Yang, a professor of political science at National Taiwan University, said the mainland's rise and its growing regional and international role would inevitably force the acceleration of cross-strait economic integration. 'Taiwan has a strong sense for the pursuit of self-determination, but this pursuit of independence is challenging the peace and pursuit of economic development in the Asia-Pacific region,' he said. 'Taiwan independence was born in a bad time, a time when the mainland is gaining acceptance as a regional and global leader.' US President George W. Bush's recent opposition and warning over Taiwan President Chen Shui-bian's proposed defensive referendum was a clear sign that the US had ditched its 'strategic ambiguity' policy towards Taiwan, the professor said. Since the US switched recognition from Taipei to Beijing in the mid-1970s, Washington has committed itself to protecting Taiwan through the sale of defensive weapons to the island. The US, however, left it vague on whether it would send troops to defend Taiwan against potential mainland aggression. Although the US said that it 'does not support' the island's independence, it never said it 'opposed' Taiwan independence either. Known as strategic ambiguity, the policy gave Washington the maximum leverage to keep pressure on the mainland to prevent it from taking a pre-emptive strike against the island, which remains a US military ally. Soon after the incident in April, 2001 when a US spy plane was forced to land in Hainan after a mid-air collision with a mainland fighter plane, Mr Bush took an even harder line against the mainland when he said he would do 'whatever it takes' so that Taiwan could defend itself. However, Sino-US relations have improved considerably since the September 11 terrorist attacks on the US, which made Washington realise that it needed Beijing's help in its global war against terrorism. Mr Bush said last month during Premier Wen Jiabao's visit to the White House that the US 'opposed any unilateral action from either side that would change the status quo' of the Taiwan Strait. In effect, Mr Bush's statement made it clear that Mr Chen and his Democratic Progressive Party must give up on their independence goals and be content with the fact that Taiwan is self-ruled and autonomous from the mainland, Professor Yang said. 'US-Taiwan relations are at their worst in the past 20 years. The US doesn't want to see any provocative moves or words from Taiwan. Mr Bush's statement signifies that the mainland is now more and more important regionally and internationally.' Mr Chen is fighting a tight race against the opposition, anti-independence Kuomintang in elections on March 20. He cannot afford to lose his traditional pro-independence support base.