The sentencing of a prominent U.S.-trained human rights lawyer to 30 months in prison in a tax evasion case by a Hanoi court on Wednesday could hit U.S.-Vietnam relations. Le Quoc Quan, 42, is one of Vietnam's best-known activist-blogger. Following the sentencing, the U.S. Embassy in Hanoi issued a statement accusing Vietnam of using tax laws for political ends and urging the government to release other political prisoners.

Accordingly to reports, Mr Quan was arrested last December while on his way to drop his daughter off at school. He has earlier posted an article on his blog criticising the role of the Communist Party and its hold on power in Vietnam.

The court ruled Mr Quan guilty of evading payment on $30,000 in corporate income tax. Describing himself as being the victim of "political plots," Mr Quan maintained his innocence throughout the half-day-long court proceedings.

"If the court represents justice, then find me innocent," he said.

Reacting to the conviction, the U.S. Embassy in Hanoi said the use of tax laws by Vietnamese authorities to imprison government critics for peacefully expressing their political views is disturbing.

"We call on the government to release prisoners of conscience and allow all Vietnamese to peacefully express their political views," the embassy statement said.

Mr Quan's lawyer, Ha Huy Son, meanwhile, said that his client will appeal the conviction. "I myself found that the evidence that the prosecutors presented wasn't really convincing," Mr Son commented.

Internationally, Mr Quan has come to symbolize the fate of dissidents in Vietnam. Reports said, Vietnamese authorities appeared worried about Wednesday's trial drawing more public protests. Security in the area was tight, with hundreds of police personnel on the streets. His supporters, meanwhile, rallied at a nearby Roman Catholic church, chanting for justice. This is not the first time Mr Quan has faced Vietnam's authoritarian law.

Mr Quan was earlier arrested in 2007 after he returned from a U.S. fellowship at the National Endowment for Democracy. U.S. Senator John McCain and former Secretary of State Madeline Albright had then urgued Vietnamese authorities for his release. He was released three months later. Mr Quan was detained again in 2011 for attempting to witness the trial of another dissident activist.

Reports say at least 46 activists, including many bloggers, have been jailed for criticizing the leadership of Vietnam's Communist Party in 2013. This figure is more than the figures in 2012. In July 2013, Reporters Without Borders ranked Vietnam second only to China in the number of bloggers arrested.

Others have been targeted in tax evasion cases, including Nguyen Van Hai, better known by his pen name, Dieu Cay, which means clay pipe, who was charged in 2008.