Vietnam has granted early release from prison to one of its most prominent dissidents, the Catholic priest Father Thadeus Nguyen Van Lym.

The release was timed deliberately for the visit of US President Barack Obama.

Father Nguyen Van Ly was imprisoned in 2007 for eight years after he was convicted of spreading propaganda against the state. 

The Catholic Archdiocese of the central city of Huê welcomed the return of the priest, now aged 70, who is frail and suffered health problems in prison. He had already served previous terms in prison and under house arrest for promoting political and religious freedoms in the communist nation, Crux Now reports.

He was first jailed in 1977, two years after Vietnam fell to communist rule. Vietnam wants the US to lift its arms embargo but there are still many people in the US concerned about the country's treatment of dissidents. 

Relations between the Catholic Church and the Vietnamese government have been difficult for many years.

Gabrielle Price of the US State Department said: "We consistently have called for the release of Father Ly and all other prisoners of conscience in Vietnam. We remain deeply concerned for all prisoners of conscience in Vietnam."

"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."