The US is set to refuse a request from Taipei to allow Annette Lu, Taiwan's vice-president, to make a transit stop in New York as part of an international tour later this month.

The decision underlines the limits of a recent warming in unofficial ties between Taipei and Washington - as well as a US desire to avoid offending mainland China, which claims sovereignty over Taiwan and fiercely objects to any international trips by the island's leaders.

Beijing last month strongly protested against a transit stop to Los Angeles by Chen Shui-bian, Taiwan's president, but Ms Lu's visit is even more sensitive. The vice president has long been a vocal defender of Taiwan's claim to a separate identity, an approach that has prompted Chinese state media to label her "scum", "traitor" and "lunatic".

Taiwan had called on the US to grant Ms Lu treatment similar to that accorded former Vice-President Lien Chan, who made a one-night stopover in New York in 1998. However, a senior official at the presidential office said yesterday Washington had made clear it was not ready to allow Ms Lu, who begins a week-long visit to Central America on September 24, to pass through New York.

"We are still discussing the issue. .. but the best scenario now is that the vice-president will be able to make a transit stop in Los Angeles," the official said.

In the strange world of diplomatically isolated Taiwan's unofficial relations with the US, even the choice of city through which a top leader is allowed to pass is loaded with political significance.

Washington bars all official contacts with senior Taipei leaders.

For the US, Ms Lu's choice of New York as a transit point was particularly sensitive, given her passionate desire for Taiwan to win entry to the United Nations and her reputation for having little time for diplomatic niceties.

However, the decision to deny Taipei's request is likely to anger members of the US Congress, some of whom have already been campaigning for Taiwanese leaders to be given greater freedom to visit the US.