Clashes between security forces and demonstrators followed strikes in Zhanaozen in December. At least 15 people were killed. A video circulated on YouTube shows demonstrators apparently getting shot by riot police, though security officials claimed victims were struck by ricochets.
Human Rights Watch said it appeared Kazakh authorities were trying to silence government critics despite promises of a transparent investigation into December violence.
U.N. High Commissioner for Human Rights Navi Pillay said from Astana there was evidence to suggest authorities used excessive force during the "tragic events" in December. A precise narrative of the events, she added, has so far proved "elusive."
"Allegations of torture and forced confessions do not seem to have been properly investigated, and there are many serious question marks over the fairness of judicial processes, and the conduct of trials (related to the incident)," she said in a statement.
Kazakh President Nursultan Nazarbayev had said labor disputes and "criminal plots" are separate matters.
Pillay added it wasn't clear who gave the order to fire on the demonstrators.