BEIJING - CHINA'S top court has approved the death sentence of a scientist accused of passing information to Taiwan, making his execution imminent, his daughter said on Wednesday as she appealed for mercy.

'A court official told us that the death sentence has been confirmed by the Supreme Court, so the execution could be very soon,' Ran Chen, daughter of Wo Weihan, who was sentenced to death in May last year, told AFP.

'We think it could happen tomorrow (Thursday).' Ms Chen has been told by a Beijing court that she can visit her father on Thursday morning, she said.

'This will be the first time in four years that we have been allowed to see him and I fear it will be the last time I see him,' the obviously distressed Ms Chen said.

The Beijing court refused to immediately comment on the case when contacted by AFP.

Wo, a 59-year-old medical scientist and a Chinese citizen who previously lived in Austria, was detained in early 2005.

His case has drawn worldwide attention with Austrian President Heinz Fischer and US Secretary of State Condoleezza Rice appealing directly to Beijing to spare him.

As the case deals with leaking state secrets, court documents are vague and the charges are unclear, said Ms Chen, an Austrian citizen and married to an American.

'We don't understand the full extent of the charges that he passed top secrets to Taiwan, the top secrets are not listed,' Ms Chen said.

'One charge that was listed said that he might have talked about senior leaders' health, the verdict says 'might.' Is this what they are going to execute him for?' China has long considered the health of its leaders state secrets. Leaking the information is punishable by death.

Wo was also convicted of passing on materials copied from Chinese military magazines that were publicly available in libraries, she said, as she desperately called for her father's life to be spared.

'We are appealing to anyone who can help keep him alive, including the Taiwan government,' Ms Chen said.

'We want his death sentence to be commuted.' London-based rights group Amnesty International is urging governments and individuals to appeal to China's parliament to extend a stay of execution to Wo.

China and Taiwan split at the end of a civil war in 1949. China regards the island as a renegade province that must eventually be reunified, by force if necessary. -- AFP