HANOI, Vietnam — Vietnam released one of its leading democracy activists from prison Monday after the dissident Catholic priest spent three years and suffered two strokes in solitary confinement, his lawyer and sister said.

Authorities released Father Nguyen Van Ly from a prison near Hanoi at 4 a.m. and drove him in an ambulance back to his hometown of Hue, his sister, Nguyen Thi Hieu, told The Associated Press.

"I'm very glad to see him out of prison and pleased to see that he is in better health than he was when I last saw him," Hieu said.

In 2007, Father Ly was sentenced to 8 years in prison for disseminating anti-government propaganda during a dramatic trial in which police muzzled him for shouting anti-communist slogans and accusing Vietnamese officials of practicing "the law of the jungle."

Father Ly is one of Vietnam's best-known human rights activists and has spent more than 15 years in prison since 1977, according to Freedom Now, a Washington-based law firm that serves as Ly's international counsel.

"We're beyond delighted that Father Ly has been released," said Maran Turner, Freedom Now's executive director. "But Vietnam still has many human rights challenges. The government is still imprisoning many other activists."

In recent months, Vietnam has sent 16 democracy activists to jail in one of its harsher crackdowns on dissent. Some observers have speculated that the crackdown is part of political jockeying ahead of next year's Communist Party congress.

Turner said she was not sure why the government had decided to release Ly now.

"It's hard to understand what moves governments to finally do the right thing," she said. "This has been a long time coming."

Vietnamese government officials could not immediately be reached for comment.

Officials at the U.S. embassy, which has pressed for Ly's release, said they had seen reports that Ly was paroled so that he could seek medical treatment.

"If those reports are true, it would be a welcome humanitarian gesture," said David Moyer, an embassy spokesman. "We don't yet have any specific information about the conditions of his release."

Father Ly is partly paralyzed on the right side of his body but can walk with a cane, according to his sister, who said he is staying at the Archdiocese of Hue, where priests planned to call doctors to assess his health.

He suffered strokes in July and November and for a time was unable to walk, Turner said. Before his release, he received treatment in a Hanoi hospital, where he was watched by five guards, she said.

In July, 37 U.S. senators sent a letter to President Nguyen Minh Triet calling for Ly's release