Michael Nguyen, a US citizen sentenced last year to 12 years in a Vietnamese jail for "attempting to overthrow the state", has been released and returned to his home in California, a family spokesman told Reuters on Monday.
Nguyen, who was born in Vietnam in 1964 and has lived in the United States since he was a child, was detained in July 2018 on suspicion of engaging in anti-government activities, including the alleged incitement of protesters to attack government offices, state media reported at the time.
"He arrived home in California this past Thursday," family spokesman Mark Roberts said in an email. He was unable to provide any further details.
Both the US Embassy in Hanoi and Vietnam's foreign ministry did not immediately respond to requests for comment.
Nguyen lost his appeal last year and his family maintained he was innocent.
Phil Robertson of Human Rights Watch said Washington had regularly raised Nguyen's detention in bilateral meetings with the government.
"The message in Michael's release is public and private pressure on the Vietnam government works when it is consistently applied on cases of dissidents who should never have been arrested, much less imprisoned, in the first place," Robertson said.
Despite sweeping economic reform and increasing openness to social change, Vietnam's ruling Communist Party retains tight media censorship and does not tolerate criticism.
Vietnam has in the past agreed to free some imprisoned political activists before the end of their sentences, provided they permanently leave the country.
In February 2019, Nguyen's wife, Helen, attended US President Donald Trump's State of the Union speech.
She was a guest of US Representative Katie Porter, a Democrat who represents part of Orange County, California, where the Nguyen family lives.
Nguyen's release was not reported in Vietnam's state media. It was not clear if two Vietnamese nationals detained at the same time were also released.