HANOI, Vietnam » A Vietnamese appeals court Thursday reduced the sentences of two land-rights activists convicted of trying to overthrow the government while upholding the sentences of two others, a lawyer said, in the latest of several crackdowns on dissidents.

The four had tried to help people in the southern Mekong Delta fight for rights to lands their families have used for generations and to challenge property seizures.

Their case follows those of several other high-profile pro-democracy dissidents who were sentenced or returned to jail in recent weeks in Vietnam, drawing sharp criticism from the U.S., France and international rights groups. The Hanoi government tolerates no threat to its Communist Party rule.

"Judging by their rolling crackdown on those who express dissenting views, Vietnam’s leaders seem to think they can sign international human rights treaties with invisible ink," Phil Robertson, deputy Asia director of Human Rights Watch said in a statement Thursday.

Thursday’s half-day appeals trial was conducted in Ben Tre by judges from the Ho Chi Minh City-based People’s Supreme Court of Appeals.

Duong Kim Khai, a pastor at a Mennonite church that’s unrecognized by the government, got his six-year sentence cut by one year, while activist Cao Van Tinh’s five-year term was reduced by six months, said Khai’s attorney Doan Thai Duyen Hai.

Meanwhile, the court upheld the eight-year sentence against Tran Thi Thuy and the seven-year jail term against Pham Van Thong, he said.

The four activists were sentenced in May along with three others, who did not appeal their sentences.

Washington condemned the convictions, saying no one should be punished for peacefully expressing their beliefs while expressing concerns that the defendants were not given legal representation prior to the trial.

The court also upheld five years of house arrest for Khai, Thuy and Thong, and four years of house arrest for Tinh after they serve out their sentences, Hai said.

The seven activists were convicted of possessing and distributing anti-government documents and attending training courses on nonviolent struggles organized by the banned Viet Tan, known as the Vietnam Reform Party, in Thailand and Cambodia from August 2009 to April last year, according to local state media reports.

They were arrested between August last year to early this year. Khai is the leader of the "Cattle Shed" congregation, which began worshipping in a barn after authorities shut down their other church.

The California-based Viet Tan is considered a terrorist organization by Vietnam, but the group says it’s an organization that promotes democracy through peaceful means. The U.S. has said it has found no evidence that the group is involved in terrorist activities.

The court alleged six of the seven defendants were members of Viet Tan.