VIETNAM'S communist authorities stirred up a storm of discontent this week when judges sentenced a dissident lawyer, Cu Huy Ha Vu, to a lengthy prison term for his activism.

Now, to the Vietnamese government's further disquiet, it seems the lawyer's disparate supporters are increasingly uniting to ridicule the draconian prosecution and sentence.

Last year's clumsy and sensationalist arrest of Dr Vu - detained, shirtless, in a Ho Chi Minh City hotel room with a woman who was not his wife - had already backfired. Salacious reports and demeaning photos appeared in the press, but Vietnamese from all walks of life nevertheless flocked to Dr Vu's support.

Dr Vu's lawyer wife, Nguyen Thi Duong Ha, his sister, and various well-connected relatives have peppered the authorities with letters and legal demands, and they have spoken freely to journalists.

Thousands of ordinary Vietnamese have signed petitions; prayer vigils have been held in Catholic churches, and crowds of supporters travelled to his politically charged trial on Monday (where two high-profile dissidents, Pham Hong Son and Le Quoc Quan, were arrested outside the court).

His sentence of seven years in prison and a further three under house arrest was greeted with outrage. The US and the European Union expressed concern yesterday. In Vietnam, the simmering fury on the internet continues to spread.

"This case is a high-water mark in activism, and also in government reaction to it," said Phil Robertson, deputy Asia director for Human Rights Watch. "We think there's an intensifying crackdown. The government is concerned about these disparate groups - environmentalists, Catholics, land rights campaigners - increasingly communicating with each other."

Mr Robertson said the protests began soon after Dr Vu's arrest. Anonymous bouquets of flowers were delivered to his office. When they were removed by police, they were replaced by fresh bunches.

The internet has been used a forum for the discontent, with famous bloggers weighing in and citizens scornfully presenting their marriage certificates on internet chat-rooms and social media, and joking about the two used condoms police said they found in the hotel room.

Vietnam's government is firmly on the back foot, but it has rejected international concerns. "In Vietnam, citizens' rights to democracy and freedom, including freedom of speech, are unambiguously stipulated in the constitution and other legal documents, and respected and observed in practice," Foreign Ministry spokeswoman Nguyen Phuong Nga said. "There is not a so-called 'prisoner of conscience' in Vietnam."

A legal activist, Dr Vu used his privileged position to take on Vietnamese authorities. Now 53, the son of one of the closest allies of revered Vietnamese war hero Ho Chi Minh has advised environmentalists and spoken out on religious freedom, denounced officials for alleged land confiscation and cyber-attacks on politically sensitive websites, and twice sued Vietnam's Prime Minister, Nguyen Tan Dung.

"I did not commit the crime of spreading propaganda against the state," Dr Vu told the court on Monday. "This criminal case was invented against me. This case is completely illegal."

One of his lawyers was thrown out of court; the remaining three walked out in protest, leaving him to fight on alone.

The interviews Dr Vu had given to the press were not read out in court or distributed, and after half a day of judicial proceedings he was found guilty of anti-state propaganda activities, including advocating an end to one-party communist rule.

"Born and raised into a revolutionary family, he did not sustain that tradition but instead committed erroneous acts," said judge Nguyen Huu Chinh. Dr Vu's lawyers have challenged his conviction with a petition to the Supreme Court.