A Vietnamese court upheld a prominent dissident's seven-year jail sentence on Tuesday after he accused the communist country's prime minister of orchestrating his arrest in an act of revenge.

The court rejected the appeal of Cu Huy Ha Vu, 53, after a day-long hearing.

Vu, the son of a revolutionary leader, was detained in November after twice trying to sue Prime Minister Nguyen Tan Dung over a controversial bauxite mining plan and a decree that prevented class-action petitions.

Vu was officially accused of spreading propaganda against the state -- including a call for political pluralism -- through writings, interviews with foreign media, and Internet material since 2009.

But the French-trained legal expert told the appeal hearing that Dung asked the Ministry of Public Security to build a case against him, because the lawsuits caused the prime minister to lose face.

"There are revenge reasons here," Vu told the court, according to a foreign journalist who watched the proceedings on closed-circuit television from a separate room.

AFP, along with other foreign media organisations, was not granted access to the hearing.

Vu's original trial in April lasted half a day and sparked deep concern among Western nations, while Amnesty International dismissed it as a "sham".

The case led to an "unprecedented outpouring of popular support" across diverse sectors of society, much of it online, US-based Human Rights Watch said in a report.

The rights group has alleged Vu was jailed for "political reasons" and said the outcome of the appeal would "have important repercussions for the rule of law and freedom of expression in Vietnam".

Vu was arrested as political tensions rose ahead of the Communist Party's secretive leadership congress in January, which confirmed Dung in office for a second term.

During Tuesday's hearing, Vu proclaimed his innocence and said he did not oppose the Communist Party -- only its leadership.

"My purpose is to protect my country's interests... I am ready to go to prison," Vu told the tightly-guarded court in the capital Hanoi, where uniformed and plainclothes police sealed off several surrounding blocks.

A few of Vu's supporters gathered outside the security cordon with signs proclaiming his innocence, but a witness said one person was dragged away by police.

At least three city buses were on standby, ready to cart people off in the event of mass arrests.

After Vu's conviction in April the United States said his case raised questions about Vietnam's commitment to reform, while the European Union said Hanoi's international reputation was at stake.

The appeal hearing came one week after Dung was formally named to his second term in office, which activists fear heralds a tougher climate for dissidents in the one-party state.

Vu is the son of Cu Huy Can, who was a celebrated poet and a member of revered founding president Ho Chi Minh's provisional cabinet from 1945.

Although the ruling 14-member Politburo agreed to Vu's arrest, other high-ranking officials had reservations because of his family history, according to a foreign diplomat.

"In Vietnam no one is punished for expressing their opinions. Only violators of the law are punished," foreign ministry spokeswoman Nguyen Phuong Nga said last week.