US officials say an American citizen has been detained in China on suspicion of espionage, amid continuing tension between the two countries.

The man, Wu Jianming, is reportedly being held in the southern city of Shenzhen, accused of spying for Taiwan. US diplomats say he was detained on 8 April and was seen by consular officials last weekend.

The Chinese authorities said he was detained on suspicion of "collecting information harmful to state security".

China's arrest of Mr Wu is the latest in a string of detentions of intellectuals with foreign ties.

Inconclusive talks

It also follows another round of inconclusive Chinese-US talks on the US spy plane, which Washington wants returned.

The fate of the spy plane is crucial to the talks

The US State Department has issued what correspondents describe as an unusual warning to Americans of Chinese origin planning to travel to China.

It said they could risk detention if they had ever been critical of the Beijing's policies.

The statement added that visiting Taiwan, or other links with the island - which China considers a renegade province - was sometimes seen by Beijing as tantamount to spying.

Tiananmen Papers

Human rights activists in Hong Kong say Mr Wu's arrest is believed to be linked with the publication of the Tiananmen Papers in the United States late last year.

China has suggested that the Tiananmen Papers were fake

The book - about China's 1989 crackdown on pro-democracy demonstrators - detailed a split in the Chinese leadership over how to tackle the protests.

Mr Wu, 46, left China for the United States in 1988. He had previously worked as an instructor at the Communist Party's Central Party School, according to Frank Lu, a human rights activist in Hong Kong.

Earlier this week 350 academics from around the world wrote to China's leaders urging the release of those detained.

Gao Zhan, a Chinese sociologist who holds US residence rights, was detained in February and has now been charged with espionage. Her husband says China was suspicious of her visits to Taiwan - but he insists she was only carrying out research on women's issues.

China is also holding:

• Li Shaomin, a US citizen who teaches business studies in Hong Kong and whose father was a liberal official ousted after the 1989 crackdown;

• Qin Guangguang, another US green card holder who worked for a US medical group;

• Xu Zerong, a historian based in Hong Kong.

The BBC's Duncan Hewitt in Shanghai says Beijing's sensitivities towards both the US and Taiwan mean that Taiwanese natives with links to either are often regarded with suspicion by Beijing.

Arms for Taiwan

The issue is particularly delicate given the impending decision by US President George Bush on whether to sell arms to Taiwan - something Beijing strongly opposes.

China has given pilot Wang Wei the status of a national hero

Meanwhile, China is demanding the return of Zhang Hongbao, leader of the outlawed Zhonggong spiritual movement. He is currently seeking political asylum in the US.

US officials left China on Friday after inconclusive talks on the spy plane. It made a forced landing on Hainan Island on 1 April after a collision with a Chinese fighter jet.

No date was set for further talks.

"There's nothing currently scheduled. We expect to hear back from the Chinese Government," said US negotiator Peter Verga.

US officials said China made no commitment to return the $80m EP-3 plane, which is filled with top-secret surveillance equipment.

China is demanding an end to US spy flights near its coast.

Both sides still blame each other for the collision that resulted in the death of the Chinese pilot, Wang Wei, who baled out as his plane crashed into the South China Sea.

Chinese leaders are attending a memorial meeting for Wang Wei on Friday.