A court in Hanoi opened trial Thursday of six activists accused of attempting to overthrow the government as communist authorities stepped up their crackdown on dissent.

Prominent human rights lawyer Nguyen Van Dai and five others are accused of affiliating with a pro-democracy group called the Brotherhood for Democracy, which prosecutors say works with foreign and domestic organisations to oppose the state, change the political system and eventually overthrow the government.

The six face the death penalty if convicted.

“The defendants have taken advantage of the fight for ‘democracy, human rights, civil society’ to conceal the … purpose of ‘the Brotherhood for Democracy,’” the official Vietnam News Agency quoted the indictment as saying.

Prosecutors determined that Dai was the mastermind behind the group, directly building its platform, recruiting new members and seeking finance from foreign organisations and individuals, which totalled more than US$80,000, it said.

International human rights groups have called for their release.

“Vietnam is one of Southeast Asia’s most prolific jailers of peaceful activists – a shameful title no one should aspire to,” James Gomez, Amnesty International’s director of Southeast Asia and the Pacific, said in statement.

He said that 97 prisoners of conscience “that we are aware of in the country are all brave women and men who have been robbed of their freedom for nothing but promoting human rights.”

Human Rights Watch put the number of people jailed for violating national security laws at 119.

Hanoi says there are no political prisoners in Vietnam and only law breakers are put behind bars.

Dai, a co-founder of the group, and another member were arrested in December 2015, initially accused of spreading anti-government propaganda while four other members were detained last July.

Dai and four others had previously been jailed for violating national security laws.

In 2007, Dai was sentenced to five years in prison for spreading propaganda against the government but got his jail term reduced to four years on appeals. His lawyer’s license was revoked.

Foreign press and diplomats were barred from the trial, which was expected to last two days.

A group of about a dozen supporters were blocked by uniformed and plain clothes police morning as they marched toward the courthouse in central Hanoi.

The Associated Press / Agence France Presse - April 5, 2018