Updated

Vietnamese authorities released and deported on Wednesday an American pro-democracy activist detained since April, removing a thorn in relations between Washington and Hanoi.

The release of Nguyen Quoc Quan, which came after intense U.S. diplomatic pressure, contrasts with the long prison terms given to Vietnamese activists who were members of the same U.S.-based dissident group. Relations between the U.S. and Vietnam have been stalled over the issue of Hanoi's treatment of dissidents.

Quan, 59, an American citizen, was arrested at Ho Chi Minh City's airport in April after arriving on a flight from the United States, where he has lived since fleeing Vietnam by boat as a young man. Quan's family and friends say he is a leading member of Viet Tan, a nonviolent pro-democracy group that Vietnamese authorities have labeled a terrorist organization. He was detained in 2007 in Vietnam for six months, also on charges relating to his pro-democracy activities.

Quan's supporters didn't deny that he had come to Vietnam from his home in California to teach non-violent resistance to the Communist government. His lawyer and family members said earlier this month that his trial on charges of subversion was imminent, but then said it had been postponed for unknown reasons.

The Foreign Ministry said in a statement that Quan had "confessed to his crime" and asked for leniency to be reunited with his family. His lawyer was not immediately available for comment. The U.S. Embassy had no immediate public response.

Authorities initially accused Quan of terrorism, but he was later charged with subversion against the state, which carries penalties ranging from 12 years in prison to death. Earlier this month, 14 Vietnamese activists associated with Viet Tan were sentenced to up to 13 years in jail.