Human Rights Watch accused Vietnam of carrying out mass arrests, persecution and torture of ethnic minority Christians in the troubled Central Highlands, a hotbed of anti-government unrest.
In a new report, the New York-headquartered organization also criticized Cambodia's January 1 decision to reinforce its northeastern border with Vietnam in a bid to halt the flow of ethnic minority or Montagnard asylum seekers.
This, it said, comes "amidst alarming new reports of mass arrests, torture, and increasing persecution of Montagnard Christians" in the Central Highlands.
"The Vietnamese government's mistreatment of Montagnards continues unabated," Brad Adams, executive director of Human Rights Watch's Asia Division, said in an accompanying statement.
More than 1,000 Montagnards fled the Central Highlands to Cambodia after security forces put down protests in February 2001 calling for religious freedom and return of ancestral lands.
In April last year thousands of Montagnards again took to the streets across the impoverished region in Easter protests, triggering a brutal crackdown, according to human rights groups, and another mass exodus to Cambodia.
During high-profile tours to the Central Highlands in December, top Vietnamese officials pledged to respect religious freedom and called on local officials to encourage "peaceful and happy" Christmas celebrations.
However, Human Rights Watch said that in the weeks leading up to Christmas, police had rounded up and arrested dozens of Montagnard Christians.
In Gia Lai province alone -- one of five provinces in the Central Highlands -- police arrested 129 people between December 12 and 24, it said.
"Christmas was relatively quiet in the highlands," said Adams. "That's because hundreds of Montagnards were rounded up and spent the holiday in police detention."
Many of those arrested during the crackdown were Montagnard house church leaders who were organizing Christmas gatherings in the villages, the rights group said.
Others targeted for detention included the wives and even young children of men who had fled to Cambodia to seek asylum, as well as those suspected of being protest leaders or making contact with exile groups in the United States.
The rights watchdog cited the testimony of a man from Dak Nong province, who was arrested in April 2004 and said he was severely beaten several times by police officers trying to obtain the names of other activists.
At the district jail, police officers pulled out one of his toe nails, beat him repeatedly on his thighs with a rubber baton, and punched him in the face, knocking out one of his front teeth, the report said.
Human Rights Watch also criticized Cambodian National Police Chief Hok Lundy's decision on January 1 to increase the number of police in the border province of Ratanakiri to prevent Montagnard asylum seekers from entering.
It accused Phnom Penh of flouting its international legal obligations.
"Instead of closing its borders to asylum seekers, the Cambodian government should be working with the United Nations refugee agency to provide sanctuary to people escaping torture and arbitrary arrest," Adams said.