Pham Chi Dung, Nguyen Tuong Thuy and Le Huu Minh Tuan were convicted of "making, storing, spreading information, materials, items for the purpose of opposing the state" at a one-day trial in Ho Chi Minh City, the Ministry of Public Security said.

Dung established the Independent Journalists' Association of Vietnam in 2014, which police said had sought regime change.

Despite sweeping economic reform and increasing openness to social change, Vietnam's ruling Communist Party retains tight media censorship and tolerates little criticism.

The party, under the leadership of 76-year-old Nguyen Phu Trong, has intensified a crackdown on dissent ahead of its five-yearly congress due to be held later this month.

Dung was jailed for 15 years, and Thuy and Tuan 11 years each.

Reuters could not immediately reach their lawyers for comment.

They wrote stories to "distort and defame the people's administration, infringe the interests of the Communist Party of Vietnam and state", the ministry said in a statement.

"These are especially dangerous activities that if not stopped could hurt national security," it said.

Amnesty International said the verdict underscored the government's contempt for free media, particularly ahead of the congress.

"Even by its own deeply repressive standards, the severity of the sentences show the depths being reached by Vietnam's censors," said Amnesty's deputy regional director, Emerlynne Gil.

Ahead of the trial, Phil Robertson, deputy Asia director at Human Rights Watch, called the charges "bogus".

"If the ruling party is so assured in its leadership, it should demonstrate its confidence by respecting civil and political rights, ending its tight control of the press, and allowing independent journalists to freely voice their opinions instead of silencing them with arrest and long prison sentences," he said.

Australian Associated Press