Activists attending a forum sponsored by the Cambodian Center for Human Rights made the charges Tuesday, The Phnom Penh Post reported.
CCHR president Ou Virak alleged that police and courts were being exploited as a way of instilling fear and intimidation into the political dissidents."
Rights abuses by government officials are largely ignored, he said.
An analysis provided by forum organizers found that since 1990 15 rights activists, politicians and policy reformers had died in suspicious circumstances. Some 1,440 have been charged with a crime.
The deaths of environmental activist Chut Wutty and journalist Hang Serei Oudo were handled properly by authorities, said Am Sam Ath, senior investigator for the rights group Licadho.
Those incidents are "hugely important," he said, noting that Cambodia is now chair of the Association of Southeast Asian Nations "and a democratic country where freedom of expression should be wide open to everyone."
Phay Siphan, a spokesman for the Council of Ministers, accused the groups of linking separate incidents as a means of attacking the government.
"They can't represent the freedom of expression as a whole nationwide," he said