Human Rights Watch (HRW) is calling for the suspension of the trial in Kazakhstan of 37 people accused of involvement in the deadly disturbances in a western Kazakh oil town last year.
In a statement, the New York-based watchdog said that many defendants claim they were subjected to physical abuse while in detention.
The unrest in Zhanaozen in mid-December came after a seven-month occupation of the main square by oil workers demanding increased salaries.
A confrontation between the demonstrators and police ended with violence in which at least 16 civilians were killed.
Authorities say the disturbances were organized by people seeking to sow instability in the authoritarian-ruled Central Asian country.
HRW says it has evidence that defendants were beaten and pressured into giving statements incriminating themselves and others.
With reporting by AP