The Cambodian Center of Human Rights says police have arrested a third human rights activist in a crackdown that has drawn international criticism.
The U.S.-funded organization says its vice-director, Pa Nguon Teang, was detained Wednesday near the border with Laos.
Saturday, the director of the same organization, Kem Sokha, and a legal worker for the Center, Yeng Virak, were both arrested on charges of defamation.
Authorities have not commented on any of the arrests.
The U.S. State Department has said the arrests are part of efforts by the Cambodian government to silence its critics.
Human Rights Watch also condemned the arrests, accusing Prime Minister Hun Sen of imprisoning peaceful critics of his government.
The Prime Minister has sued several people for their criticism of a border demarcation treaty he signed with Vietnam in October.
Some information for this report was provided by AFP and AP.