WASHINGTON (AFP) — A bipartisan group of 37 US senators sent a letter Wednesday to Vietnam President Nguyen Minh Triet calling for the "immediate and unconditional release" of a dissident Catholic priest sent to jail for eight years in 2007.

The lawmakers urged Triet to intervene in the case of Father Nguyen Van Ly, who was convicted in a half-day trial in the city of Hue for spreading propaganda against the communist state.

The senators -- led by Democrat Barbara Boxer and Republican Sam Brownback -- said Ly's trial appeared "seriously flawed," stressing that the pro-democracy activist was denied access to counsel and prevented from presenting a defense.

"Given these serious flaws in relation to his arrest, trial and imprisonment, we request that you facilitate Father Ly's immediate and unconditional release from prison, and allow him to return to his home and work without restrictions on his right to freedom of expression, association and movement," the letter said.

The 63-year-old priest has been jailed three times since the 1970s for a total of 14 years, and his 2007 trial drew condemnation from diplomats, Vietnam watchers and human rights groups for the one-party state that has gone to great lengths over the past year to boost its international prestige.

The senators' letter reminded the president of Vietnam's commitment to protect the rights of criminal defendants including "the presumption of innocence, the right to present a defense and the right to counsel.

"Father Ly's arrest, trial and ongoing detention in this instance call into question Vietnam's commitment to these fundamental principles," they wrote.

Two senators who strongly supported normalization of US-Vietnam ties in the 1990s, Democrat John Kerry and Republican John McCain, a prisoner of war in Hanoi for more than five years during the Vietnam war, did not sign the letter.

The letter comes just weeks after a Vietnamese human rights lawyer, Le Cong Dinh, was arrested for "propaganda" against the state. That case has sparked concern from European countries, the United States, a global association of lawyers, human rights watchdogs and press freedom groups around the world.