The prolonged detention of the human rights lawyer, Nguyen Van Dai, has been extended until April, according to a document obtained by his lawyer.
Dai has been held in isolation, with no access to family or lawyers, since December 16 2015.
The authorities have given no indication as to when he and his assistant, Le Thu Ha, who was arrested at the same time, will be brought to trial.
Dai’s lawyer, Hu Huy Son, posted a notification from the prosecutors’ office confirming that his client’s term in a detention camp had been extended again.
It is the third such notification since Dai and Ha were arrested more than a year ago and charged with spreading propaganda against the state, under Article 88 of the penal code.
The Vietnamese authorities have been condemned by the UN and international human rights bodies for the practice of holding political detainees without trial for extended periods, denying them access to friends, family or lawyers.
Critics have said the practice leaves prisoners open to physical and mental abuse that could amount to torture.
Dai resumed his work as a trenchant advocate of democracy and human rights following his release from an earlier term of prison and house arrest in early 2015.
Harassment and intimidation
He was subjected to close monitoring by the security services, including the fixing of surveillance cameras opposite his house.
Systematic harassment and intimidation culminated in a violent attack in December, in which he was savagely beaten by plainclothes men and abandoned half naked by a roadside.
A week later, as he prepared to meet a European Union delegation, in Vietnam to discuss human rights, he was arrested at home and has not been seen since.
The police used similar tactics against the blogger, Nguyen Huu Vinh, who wrote under the pseudonym Anh Ba Sam.
He was held incommunicado for two years before finally being brought to trial in May 2016.
He was sentenced to five years in prison on a charge of “abusing democratic freedoms” to damage the interests of the state, a charge also frequently used by the authorities to silence critics.
The vigour of the government’s efforts to crush leading figures in Vietnam’s nascent civil society movement appears to indicate a degree of insecurity in the Communist party.
Despite repeated appeals from UN bodies, the US, EU and other trading partners, Vietnam’s leaders have chosen to ignore requests that they live up to the international conventions on human rights that they themselves have signed.
Civil society activists in Ho Chi Minh City reported last week that one of their meetings was violently broken up by plainclothes thugs, another favoured tactic of the police to intimidate government critics.
One of the activists, Nguyen Ho Nhat Thanh, said he was beaten, threatened with a gun and taken to a police station by a group of tattooed youths, according to a report by RFA.