China has acknowledged it has arrested a high-profile US-based democracy activist, Wang Bingzhang, who disappeared in Vietnam six months ago.

The authorities say he was kidnapped in Vietnam, with a ransom demand of $10m and was later found in southern China.

They say he is now facing charges of espionage and terrorist activities.

Two other activists arrested with Mr Wang, Yue Wu and Zhang Qi - who had also been reported missing - are said to have been cleared of all charges and freed.

Vanished

The three entered Vietnam - where they were planning to hold meetings with fellow activists - with valid visas on 16 June, and last communicated with their families on 26 June.

They have not been heard from since.

Chinese dissidents in the United States said in July that they had received information that the three were abducted by Chinese security forces along the border of China and Vietnam and were being held at a secret location in China.

But China's official news agency Xinhua said on Friday that police had found the trio bound and gagged in a temple in Fanchenggang city, southern Guangxi province, on 3 July.

It said they had been kidnapped on 27 July in Tinh Quang Ninh in Vietnam, and were being blackmailed.

After they were found, Mr Wang was transferred to neighbouring Guangdong province, where he was put under house surveillance before being formally arrested on 5 December, the agency said.

"The state security department had verified that Wang, starting in the early 1980s, had struck up contact with Taiwan's espionage organisation, which paid him as he collected and stole state secrets," it said.

Mr Wang has lived in Canada and the US since 1979.

Xinhua quoted a spokesman from the ministry of public security as saying that Mr Wang was also facing charges of engaging in "violent terrorist activities".

His colleagues in the democracy movement say he has never committed a violent crime.

Exiled

Fang Yuan, a member of the China Democracy Party, which is outlawed inside China, has said the disappearance of the dissidents was "testament to the desperate lengths the government will go to stop the evolution of democracy in China".

The three all have connections with exiled Chinese opposition groups:

• Wang Bingzhang was jailed twice in China during the Cultural Revolution for speaking against the government. He moved to North America in 1979, founded the magazine China Spring, and organised the Chinese Alliance for Democracy in New York. He made headlines in 1998 for sneaking into China and getting expelled

• Yue Wu, who lives in Paris, was a labour leader in the 1989 pro-democracy protests in Beijing's Tiananmen Square

• Zhang Qi was granted political asylum in the US in 2001; she is the leader of Zhong Gong, a banned health and meditation sect, and has been wanted by the Chinese Government since 1999