Amnesty International has challenged the official Chinese version of events in Xinjiang a year ago, when nearly 200 people were killed in the regional capital, Urumqi.
At the time, China blamed the trouble on the ethnic Uighur population, saying most of the dead were Han Chinese.
But Amnesty says the security forces used an unnecessary level of force, followed by mass arrests, disappearances and torture.
Amnesty says its findings are based on interviews with Uighurs who witnessed the events.
