Vietnam has stepped up its imprisonment of political activists, Amnesty International said in a report Monday, intensifying a crackdown that has seen the number of prisoners of conscience increase by almost a third since last year.

Nearly 10 percent of the 128 prisoners held in the Southeast Asian country for expressing dissenting views were jailed for posting anti-state comments on social media platforms such as Facebook, the report said.

Amnesty defines prisoners of conscience as people who have not used or advocated violence but have been imprisoned because of their identity or beliefs.