By Agence France-Presse
Communist Vietnam routinely silences dissent with activists subject to arbitrary detention and lengthy jail spells.
The statement from the UN Human Rights Office referred to the recent detentions of Ho Van Hai, a prominent blogger, and Luu Van Vinh and Nguyen Van Duc Do -- two political activists pushing for greater freedoms in the autocratic state.
All three were arrested earlier this month and have been held incommunicado since.
Calling for their release, the statement said the UN "was also deeply concerned by reports that the activists, who have been held incommunicado in line with Vietnamese law for so-called National Security offences, have been subjected to torture".
Vietnam uses a raft of broadly worded national security laws to jail dissidents and critics. All newspapers and television channels are state-run in Vietnam and private media is banned.
But blog sites and social media forums have become an increasingly popular arena for citizens to air anti-government grievances.
Le Thi Thap, the wife of Luu Van Vinh, told AFP she has been unable to reach her husband since police came to their home in southern Ho Chi Minh city on 6 November.
"He was accused of conspiracy to overthrow the state. But my husband is a kind person. I don't know what my husband did as I never go deep into his work," she said.