Updated

Secretly moved from prison to prison, held in solitary confinement, their families subject to constant harassment -- Vietnam's activist bloggers say they are treated like international terrorists.

While Vietnam insists it has no political prisoners -- and therefore will not comment on the subject -- rights groups estimate hundreds of activists are locked up for speaking out against one-party communist rule, including at least 46 jailed this year.

Activists say that while conditions are no picnic for common criminals, prisoners of conscience face particularly harsh treatment behind bars.

Prisons have a separate area for political prisoners where "anything can happen and no one knows," said Nguyen Tri Dung, the son of high-profile blogger Dieu Cay who is serving 12 years for anti-state propaganda.

Like many dissidents, Dieu Cay -- whose real name is Nguyen Van Hai -- refused to plead guilty.

Now his relatives believe he is being punished in prison for this show of defiance.

Since he was detained in 2008 on an initial charge of tax evasion, Dieu Cay has been moved 10 times between different prisons, according to his family, who said they are never notified in advance.

The imprisoned dissident, whose case has been raised by US President Barack Obama, faces constant pressure to sign a confession as well as visitor restrictions, his relatives said.

His son told AFP that he too had been repeatedly detained by authorities -- always for less than 24 hours -- to disrupt his studies and prevent him sitting his exams.

Using vague, trumped up administrative charges is a way for authorities to warn activists to cease their campaigning, experts say.

Another prominent blogger, the Catholic lawyer Le Quoc Quan, is due to go on trial on Wednesday for tax evasion.

???Le Quoc Quan's apparent crime is to be an effective public critic of the Vietnamese government,??? New York-based Human Rights Watch (HRW) said Tuesday, calling for the 41-year-old's release.

Once in jail, the Vietnamese authorities are always strict with prisoners who do not admit their guilt, said one activist who spent five years in prison in the past.

"They fear they will influence other prisoners and cause problems," he said.

Criminal and political prisoners are held separately and treated in very different ways, he said on condition of anonymity.

"Criminal prisoners in Vietnamese jails can buy anything -- food, tobacco, heroin," he said, but political prisoners are often denied books or writing paper and held in cells on their own.

Vietnam's authoritarian government does not allow independent inspections of jails.

But experts said arbitrary periods of solitary confinement -- another measure used against political detainees -- could constitute torture under the Convention Against Torture (CAT), which Vietnam has said it will ratify this year.

"The reports that we've received indicate that it is a standard practice and that decisions to send someone to solitary confinement are arbitrary, based on the discretion of jail officials," said HRW deputy Asia director Phil Robertson.

'Isolate the activists'

'Isolate the activists'

Former political prisoners and their relatives interviewed by AFP described intense harassment of families: from pressuring friends to cut contact to denial of business licenses needed to make a living.

It is designed to "isolate the political activists... and scare family, friends," the formerly detained activist said.

"They find other ways to control, persuade or discredit (activists)," they said.

The pressure exerted on families and friends means many dissidents end up isolated from normal Vietnamese life -- which often makes them even more determined.

"Difficult people are the ones prepared to make a stand and then they get ostracised and that makes them act even more stubbornly," said Bill Hayton, author of 'Rising Dragon' who is banned from Vietnam.

The excessive reaction by authorities is counterproductive, said Hoang Nguyen, a Vietnamese student living in exile in the United States.

"Families (of activists) learn a lot about the nature of the political regime," she said, adding that many relatives "turn dissident" themselves.

Nguyen, whose fianc?? was jailed in 2010, said the Vietnamese consulate in Washington refused to renew her passport unless she promised to give up her "dissident activities".

Fighting from behind bars

She refused and was recently granted political asylum.

Fighting from behind bars

Branded an "enemy of the Internet" by Reporters Without Borders, Vietnam bans private media and all newspapers and television channels are state-run.

Even so the Internet and social media are changing the nature of the battle.

Facebook is sporadically blocked but wildly popular among Vietnamese users.

"Social media connectivity and more broad and experienced activist networks are making sure that the word from prisons gets out far and wide," said Robertson.

In June, after authorities refused to respond to a formal complaint and attempted to put him in solitary confinement for three months, Dieu Cay embarked on a hunger strike.

"He is trying to light up the real fate of political prisoners of Vietnam, which is now in the darkness," his son said.

Separately, in May, imprisoned legal activist Cu Huy Ha Vu -- the son of a revolutionary leader -- also refused to eat for 25 days.

Eventually, both detainees called off their hunger strikes after receiving key concessions -- a tactic seen by some as part of the communist rulers' strategy to manage dissent.

"China and the USSR, they purged ruthlessly their competitors, killing many, sending them into exile," said the formerly detained activist.

"The Vietnamese Communist Party is cunning, wise -- they do not see killing and imprisonment as the best solution (but) the last resort. Therefore their power may last longer."