Vietnamese police have arrested six political activists, including four foreign citizens, in Ho Chi Minh City.
The activists - two Vietnamese, two American, one French and one Thai - were reportedly arrested after attending pro-democracy discussions.
Three of the six are members of a US-based anti-communist group.
The Vietnamese government exerts strong control over media and political activity. It has not yet commented on the arrests.
The US-based organisation Viet Tan (Vietnam Reform) said the activists were arrested on Saturday after they "participated in discussions with other democracy activists on promoting peaceful democratic change".
It said their members were using examples of non-violent struggles around the world to "help empower the Vietnamese people."
Vietnam says Viet Tan, which was established by a former south Vietnamese general in 1982, is a terrorist organisation and has staged a media campaign against it in recent months.
Among those arrested was Frenchwoman Nguyen Thi Thanh Van, a well-known campaigner and contributor to overseas Vietnamese-language media.
A press officer from the US embassy in Hanoi told the BBC the US was seeking information from the Vietnamese government regarding two US nationals.
There is no word on the charges they face.
The Paris-based campaign group Reporters Without Borders has condemned the arrests.
"We call for their immediate release since they were only engaged in peacefully promoting freedom of expression," it said.
Vietnam has recently increased its efforts to silence political dissent and has jailed many activists who oppose the one party state system.