US-China relations are already frayed over the spy plane crisis

His forthcoming trip to the US looked likely to the same to Sino-US ties.

On his return from Japan, he told reporters at Taipei's Chanbla Airport that he was now postponing his imminent trip to America.

"I need some time to rest," he said, after undergoing surgery in Japan to widen blocked arteries to his heart.

'Private citizen'

China views Mr Lee as one of the foremost advocates of independence for Taiwan.

The US is going ahead with a controversial arms sale to Taiwan

Japan's decision to grant him entry for a medical check-up outraged Beijing, which has put off a visit to Tokyo by Li Peng, the second most senior figure in the country's political hierarchy.

The US said it was giving a visa to Taiwan's former president because he is now a private citizen.

Mr Lee said after his operation it would not be good for him to take such a long journey.

But his postponement comes as relations between Washington and Beijing are under strain because of America's arms sales to Taiwan and President George Bush's expressions of support for the island.