A Vietnamese court has jailed a fish farmer for three years for “plotting to overthrow the state”, a court clerk said on Wednesday.

Vo Viet Dzien, 41, was handed the sentence on Tuesday for plotting to overthrow the state and disrupt the communist country’s celebrations of the April 30, 1975 fall of Saigon, a clerk at Tay Ninh provincial court said, without giving details.

Dzien was said to be involved with the US-based Restoration Party, a little-known pro-democracy group banned in authoritarian Vietnam.

Earlier this month, 13 activists were jailed on similar charges after a court in central Nghe An province found them guilty of having links to Viet Tan -- another banned US-based group that Hanoi says is a terrorist organisation.

Rights groups say charges of spreading anti-state propaganda and attempting to overthrow the regime are routinely laid against peaceful dissidents in a country where the ruling Communist Party forbids political debate.