Late March demonstrations in Kazakhstan coincided with the 100-day anniversary of clashes between political and protesters in the western Kazakh oil city of Zhanaozen. At least 15 people were killed during last year's oil strikes.
Kazakh authorities last week charged some of the demonstrators with plotting a "forcible overthrow of constitutional order" in the country.
Mihra Rittmann, a specialist on Central Asia for Human Rights Watch, said the charges were vague and raised serious questions about judicial transparency.
"If any of these people has committed an actual criminal offense, the authorities should say what it was," said Rittmann in a statement from Berlin. "Otherwise, the charges should be dropped and the activists released immediately."
All of the accused were charged previously with stoking social unrest. Charges for some of the accused during earlier trials ranged from arson to desecrating the national flag. Two of the defendants were children.