The invitation to Defence Minister Tang will enrage Beijing, even more so because it comes immediately after what the mainland regards as a 'fruitful and substantial' visit by US President George W. Bush. For Beijing, disagreement over Taiwan is the biggest obstacle in relations with Washington, especially its supply of arms and the obligations set out in the US Taiwan Relations Act to defend the island. The Act authorises the US to sell defensive weapons to Taiwan and includes a clause saying the US will view a military assault by Beijing as a matter of great concern. Mr Bush repeated his Government's commitment to defend the island and honour the Act, both at his joint news conference with President Jiang Zemin and in a question-and-answer session at Tsinghua University. Beijing opposes any country issuing visas to members of President Chen Shui-bian's Government. It would regard the issue of a visa to Mr Tang as extremely provocative. It would be the first US visit by a defence minister since 1979 and would upgrade military exchanges between America and Taiwan. China has demanded that the US reduce the quality and quantity of its arms sales to Taiwan and eventually end them all together. Mr Tang's visit would have the opposite effect, enabling him to discuss purchases of the latest US military hardware. The news is likely to ruin the honeymoon atmosphere created by Mr Bush's visit and celebrated in official Chinese newspapers yesterday.