Former king Norodom Sihanouk has written a letter to Prime Minister Hun Sen asking him to intervene in the case of a defrocked, disappeared monk.
Rights groups say the monk, Tim Sokhorn, was forcibly deported to Vietnam, and his whereabouts remain unknown.
Cambodia's Buddhist leadership defrocked Tim Sokhorn for allegedly harboring Khmer Kampuchea Krom monks at his Takeo province pagoda and stirring unrest between Cambodia and Vietnam.
Thach Setha, director of the Khmer Kampuchea Krom Association, has also written the prime minister asking for his intervention in the case.
Hun Sen adviser Om Yentieng declined to comment Tuesday.
Government spokesman Khieu Kanharith could not be reached for comment Tuesday but has said in the past the defrocked monk had affairs with women, a charge Khmer Krom groups deny.
Rights workers say Tim Sokhorn was last seen being shoved into a car, while the Minsiter of Interior says he was sent to Vietnam at his request.