BEIJING- A FORMER Tiananmen prisoner has been detained and other Chinese dissidents placed under house arrest or tight surveillance ahead of the 20th anniversary of the crackdown, activists said on Tuesday.

Wu Gaoxing, who was jailed for two years after he protested in 1989 in the eastern province of Zhejiang as pro-democracy protests were taking place in Beijing, was taken away Saturday, fellow activist Chen Longde told AFP.

Wu had just written an open letter to Chinese President Hu Jintao seeking economic redress for those jailed after the army crackdown on and around Tiananmen Square on June 4, which killed hundreds and possibly thousands.

Chen, who himself was jailed for three years and signed the letter along with three other former prisoners, said they wanted the government to resolve their living problems, which included a lack of health insurance.

'We were also fired from our companies,' he said over the phone. 'For 20 years, they have deprived us of our right to life.'

Chen said he and the three other signatories had not been bothered by police, and believed Wu had been detained because he wrote the letter.

In Beijing, meanwhile, Ding Zilin, a 72-year-old woman whose son was shot and killed in the crackdown on the evening of June 3, said she had been asked to leave the Chinese capital ahead of the anniversary.

'But I refused,' she said, adding she had been followed Tuesday when she left her house to buy things to mark her son's birthday, which would have been on June 2, and his death the next day.

In the southwestern province of Guizhou, human rights activist Chen Xi told AFP he had been put under house arrest, and fellow dissidents in Guiyang, the provincial capital, were under strict surveillance.

The latest crackdown on dissidents came after Bao Tong - a former aide to late Chinese leader Zhao Ziyang, who was purged for sympathising with pro-democracy protesters - was taken out of Beijing last week. -- AFP