A Vietnam court has jailed seven activists agitating for land rights and religious freedom for up to eight years, a US-based group said, in the latest of a series of verdicts against dissidents. The United States said it was \"troubled\" by the convictions, on charges of attempted subversion, against peaceful activists. In a statement late Monday, the US-based opposition organisation Viet Tan said the heaviest sentence of eight years went to its member Tran Thi Thuy, 40, while two other Viet Tan members were also jailed. Duong Kim Khai, 52, received a six-year term while Nguyen Thanh Tam, 58, got two years. Four other activists were jailed for between two and seven years, said Viet Tan, also known as the Vietnam Reform Party. It said they were convicted after a one-day trial on Monday. Court officials told AFP they had no information about the case. Amnesty International says dozens of political critics and activists have been jailed in the authoritarian state since late 2009, including people who have called for a multi-party political system. Viet Tan said the \"pre-determined\" sentencing was an attempt to silence people who \"spoke out against the regime\'s failings\". The accused are all land rights activists and include a Mennonite pastor, Khai, who is a veteran advocate on behalf of dispossessed farmers in the Mekong Delta, Viet Tan said. Two others are also Mennonite evangelists. Most were arrested between July and November last year, Viet Tan said, adding that all were convicted under Penal Code Article 79 based on their \"affiliation\" with the opposition group. They faced a maximum possible sentence of 15 years in prison. Viet Tan said the activists had attended courses on non-violent struggle and distributed slogans about two disputed South China Sea archipelagos over which Vietnam has a long-running sovereignty dispute with China. The accused went to Thailand and Cambodia between August 2009 and March 2010 for training in how to overthrow the government non-violently, said an indictment cited Tuesday by state-controlled Tin Tuc newspaper. It said they \"abused democratic rights\" by organising demonstrations and causing disturbances and that their behaviour was \"dangerous, violating national security\". Viet Tan calls itself non-violent and pro-democracy, but Vietnam -- a one-party communist state -- labels it a \"terrorist group\". Land disputes and complaints that residents have been cheated out of compensation have become the most common cause of protests in Vietnam, a mainly rural country that is rapidly industrialising. \"The US is troubled by the conviction of these seven activists in connection with their efforts to advocate peacefully on behalf of land-use protesters\", a spokesman for the United States embassy told AFP. \"We are particularly concerned by reports that several of the defendants were denied access to legal representation prior to their trial.\" A group of US lawmakers has described the case as \"a stain\" on Vietnam\'s religious freedom record. Vietnam says it has achieved significant progress on human rights.