United Nations human rights Chief Navi Pillay on Tuesday called on China to reveal the truth about the army's violent suppression of mass pro-democracy protests on Beijing's Tiananmen Square 25 years ago.
She also urged the Chinese authorities to release dozens of people reported to have been arrested in the run-up to the anniversary, which falls on 4 June, and to stop blocking Internet discussion of the events.
"It is in the interests of everyone to finally establish the facts surrounding the Tiananmen incidents", said Pillay, a former high court judge in South Africa and justice of the International Criminal Court.
In the absence of an independent, factual investigation, much remained unknown about what happened and estimates of how many demonstrators, largely students and workers died ranged from hundreds to thousands, she noted.
Families of many of those who were killed were still waiting for an explanation of what had become of their loved ones.
Since the sudden crushing of the weeks-long protests in the heart of Beijing, which had continued during a visit by reforming Soviet leader Mikhail Gorbachev, and in other cities, China has sought to erase them from its history.
It has come down hard on any attempt to mark the anniversary inside the country both publicly and privately. But Pillay, formally UN High Commissioner for Human Rights, said it was very important to establish a truth-seeking process.
"Rather than stifle attempts to commemorate the 1989 events, the authorities should encourage and facilitate dialogue and discussion as a means of overcoming the legacy of the past", she declared in a statement from her Geneva office.
"Learning from events of the past will not diminish the gains of the past 25 years, but will show how far China has come in ensuring that human rights are respected and protected", she said.
China defended the 1989 crackdown on Tuesday, the eve of the 25th anniversary, saying it had chosen the correct path for the sake of the people.