Seven weeks of protests preceded the crackdown

The dissidents, from the north-eastern Jilin province, also demanded compensation for victims' families and for the thousands of people imprisoned in the crackdown, and urged the government to reverse its verdict that the 1989 demonstrations were a "counter-revolutionary rebellion" that had to be quelled.

The call for a government rethink of the bloody crackdown was also echoed by veteran Chinese democracy campaigner Ren Wanding.

"The day 4 June is rehabilitated will necessarily be the day of democracy," he said. "I wish success to every commemorative activity to pay silent tribute to those who laid down their lives and to salute freedom."

Tight security

To prevent commemorations, Beijing authorities have stepped up security and extra military police have been patrolling Tiananmen Gate, which overlooks the square.

Ren Wanding said police had visited his home on Friday and "told me not to carry out any activities".

Hundreds were injured when the demonstration was crushed

Friends of Ding Zilin, a prominent campaigner for victims of the crackdown and whose 17-year-old son was killed, said plainclothes police were stationed outside her house and that her phone had been cut off.

Families of those who died in the crackdown were planning quiet memorials.

Su Bingxian, whose 21-year-old son was killed with three bullets to the chest, said she, her husband and their surviving two children would spend Saturday evening together in commemoration.

Zhang Xianling said she had placed flowers under a portrait at home of her 19-year-old son who was killed and would visit his grave on Sunday.

Human rights

The 4 June anniversary is also being marked in Taiwan, which sees itself as a role model for democracy in China.

The island's new President, Chen Shui-bian, has pledged to pursue an offensive of human rights diplomacy internationally, but human rights activists in Taiwan are urging him not to shy away from raising human rights issues with China.

Yang Tai-sun, deputy secretary-general of Taiwan's Association for Human Rights, said: "As a human rights organisation we feel very excited about this call, but we want to remind President Chen Shui-bian that in promoting human rights, he should not ignore the human rights situation over the Taiwan Straits.

"He may consider that to promote the human rights situation in China might jeopardise the stability of the two sides, but we think differently.

"We believe that using the topics of human rights could establish a bridge between the two peoples."