The United States has urged China to free all those still in prison 23 years after Beijing's crackdown against protesters in Tiananmen Square.
The US State Department also called on China to "provide a full public accounting of those killed, detained or missing".
In 1989, the Chinese military shot dead hundreds of civilians rallying for democracy .
Chinese authorities have made any discussion of the 1989 unrest taboo, the BBC reports.
Beijing considers the events a counter-revolutionary revolt and defends its response.
The army dispersed pro-democracy demonstrators on 3 - 4 June 1989 using tanks and live ammunition.
Afterwards the authorities claimed no-one was shot dead in the square itself. There is still debate about exactly how many people were killed. Some say a few hundred, others say a few thousand.
Human rights group the Dui Hua Foundation estimates that fewer than a dozen activists arrested in the Tiananmen crackdown remain in jail. Hundreds were rounded up at the time.