WASHINGTON (Reuters) - The United States said on Friday it was deeply concerned by the sentencing of a Vietnamese dissident to 20 years in prison this week, calling a trend of increased arrests and harsh sentences for peaceful activism troubling.

Vietnamese environment activist Le Dinh Luong listens to the verdict during his trial at a court in Nghe An province, Vietnam August 16, 2018. VNA/Bich Hue via REUTERS

A U.S. State Department statement on the sentencing of Le Dinh Luong after a one-day trial on Thursday called on Vietnam to release all prisoners of conscience immediately.

Luong, 53, was arrested last year after encouraging people to boycott a National Assembly election, writing Facebook posts that expressed views against the ruling Communist Party and state, and inciting protests against a Taiwanese steel firm. He was charged with attempting to overthrow the state.

“The trend of increased arrests and harsh sentences for peaceful activists in Vietnam is troubling,” the State Department said.

“The United States calls on Vietnam to release all prisoners of conscience immediately and to allow all individuals in Vietnam to express their views freely and assemble peacefully without fear of retribution.”

Despite sweeping economic reform and increasing openness to social change, Vietnam’s Communist Party retains tight media censorship and does not tolerate criticism.

The United States has developed close ties with Vietnam in recent years, seeing it as an important regional partner in the face of China’s rapid rise, but Washington has remained critical of Hanoi over human rights.

It has also criticized Hanoi over a cybersecurity law that tightens control of the internet and global technology companies operating in the country, raising fears of economic harm and a further crackdown on dissent.

Vietnamese state media cited police as saying that Luong was a “dangerous” member of Viet Tan, a U.S.-based human rights group that Vietnam regards as a “terrorist” body.

New York-based Human Rights Watch has called the charges against Luong politically motivated.