The Vietnamese authorities have jailed three bloggers accused of spreading anti-government propaganda, in a case criticized by human rights groups.

The high-profile but brief trial took place in Ho Chi Minh City under heavy security, reports say.

The trio was given jail sentences of between four and 12 years.

The government, which does not allow freedom of expression, has been under pressure from bloggers over corruption cases and human rights issues.

The three were accused of posting political articles on a banned website called Free Journalists’ Club, as well as articles critical of the government on their own blogs.

Vietnam has jailed three bloggers accused of spreading anti-government propaganda

Nguyen Van Hai, who uses the pen name Dieu Cay, received the longest sentence of 12 years.

The case of Dieu Cay, who was a soldier before he became a dissident writer, was raised by US President Barack Obama earlier this year.

Former policewoman Ta Phong Tan, who also wrote a blog called ”Justice and Truth”, was sent to jail for a decade. In July, her mother died after setting herself on fire in apparent protest against the detention of her daughter.

The third dissident writer, Phan Thanh Hai, was jailed for four years.

In a statement, the US embassy in Hanoi called on the Vietnamese government to free the group.

“We are deeply concerned by reports that the Ho Chi Minh City People’s Court convicted and sentenced blogger Dieu Cay to 12 years in prison for peacefully expressing his political views,” the statement said.

Activists have accused the government of stepping up a crackdown against bloggers and peaceful activists.

“Vietnam’s arbitrary use of vaguely worded national security laws to imprison critics of the government means bloggers are bearing the brunt of this assault on freedom of expression,” Brad Adams, Asia director at the New York-based Human Rights Watch, said in a statement urging the release of the trio.

Earlier this month, Vietnam’s prime minister hit out at three blogs critical of the government.

A statement on a government website said PM Nguyen Tan Dung had ordered police to investigate and take action against those responsible.