On the 15th anniversary of China's violent suppression of pro-democracy demonstrators in Beijing's Tiananmen Square, human rights advocates are renewing their demands for justice for the victims. The London-based human rights group, Amnesty International, has joined the calls Thursday.

Every year since 1989, Amnesty International has called on the Chinese government to allow an independent inquiry into the killing of unarmed demonstrators by government troops in and around Tiananmen Square. Every year, the government has ignored the group's calls, and refused requests to meet with its representatives.

Amnesty's Louise Vischer says her group maintains hope that China's leaders will eventually provide redress to the families of victims and to the outside world, which she says is still horrified by the pictures of government soldiers using guns and tanks against unarmed young demonstrators.

Ms. Vischer says a decision by the National People's Congress, China's legislature, to insert a human rights amendment into the Constitution last March is a positive sign.

"One of the strong messages that the Chinese could give to the world is that, if they have put into their constitution this amendment for human rights," she said. "We are asking that they at least, as a minimum, release all those who are still detained since Tiananmen. That would be a good signal to the world."

Amnesty says it has records of 50 people still detained without fair trials, but it says the actual figure is likely much higher.

Rights advocates are also calling for those who are responsible for the crackdown to be brought to justice.

Analysts say it will be a long time before the government revises its stance on the killings. Chinese officials this week repeated what they view as their justification for the crackdown, saying it was necessary in order to keep China stable and ensure the economic growth the country is now enjoying.

Meanwhile, police continued to guard Tiananmen Square for any signs of demonstrations connected with Friday's anniversary. Public mention or commemoration of that event is banned in China.