Cambodia released eight protesters hours after police detained them for demonstrating against what activists described as the politically motivated
imprisonment of a group of rights workers and an election official.
Two of the protesters were foreign men, one Swedish and one German.
They were freed on Monday night after being questioned for supporting rights activists who were jailed over an ongoing sex scandal investigation involving opposition politician Kem Sokha.
"They released us after over 10-hour detention," Ee Sarom, one of those detained, told Reuters on Tuesday.
A series of legal cases filed against prominent members of the main opposition party have raised tensions in Cambodia, where self-styled strong man Prime Minister Hun Sen has held power for 30 years.
Rights groups have accused the government of using the legal system to neutralise the opposition to give Hun Sen an advantage in the run up to the next general election in 2018.
Sam Rainsy, the leader of the opposition Cambodia National Rescue Party (CNRP), is in exile to avoid prison on charges that were reactivated last year and for which he had previously received a royal pardon.
Kem Sokha, the party's acting president in Rainsy's absence, is facing charges for defamation and procurement of prostitution after recordings of a telephone conversation purportedly between Sokha and a woman were leaked.
Six other people - including a United Nations employee — allegedly paid the woman to deny she had a relationship with Sokha, and are facing trial on bribery charges.
The UN worker has not been detained.