Vietnam freed a Catholic priest on Friday, one of its longest-serving political prisoners, just a few days before a visit by U.S. President Barack Obama in which human rights is expected to be a key talking point.

Nguyen Van Ly, who has spent most of the past two decades in detention due to his relentless pursuit of democracy and religious freedom, was released from a prison in central Hue province after his fourth stint behind bars.

“They released him in a special amnesty by Vietnam’s president before the Obama trip,” Catholic priest Phan Van Loi told Reuters by phone.

The communist country’s state-controlled media has made no mention of Ly’s release, which comes as Obama weighs whether to lift an arms embargo on Vietnam, a decision Washington has long said would hinge on human rights progress.

Loi said he met Ly after his release and that although he appeared weak, he was in high spirits.

The U.S. Embassy in Hanoi welcomed the release of Ly but said other dissidents should be freed too.

“We call on the government to release unconditionally all prisoners of conscience and allow all Vietnamese to express their political views peacefully without fear of retribution,” an embassy spokesman said.

During Ly’s long periods of incarceration, sometimes in solitary confinement, he suffered numerous health problems, including strokes and partial paralysis.

His release on Friday was three months before the end of an eight-year sentence for “anti-state propaganda,” which comes under a section of the criminal code that rights groups say is vaguely worded and used to punish outspoken critics.

The priest has been on the receiving end of some of the country’s harshest verdicts, stemming from his opposition to the political monopoly of the Communist Party. He set up a pro-democracy movement and was behind several banned publications.

Human rights is a thorny issue for Vietnam that has created dilemmas for Western governments keen to engage with one of Asia’s fastest-growing economies but alarmed by the arrests, harassment and jailing of its detractors.

Vietnam is keen to see the arms embargo removed, to give it better bargaining power in defense procurements and access to advanced United States technology, in what experts say is to counter China’s maritime assertiveness.