Authorities in Vietnam have detained a prominent journalist critical of the government on suspicion of undermining national interests.

A statement posted on the public security ministry's website says Truong Huy San and a lawyer were arrested for abusing democratic freedom through social media posts violating the state's interests.

Truong Huy San is known for his reports criticizing Vietnam's top leader -- Communist Party General Secretary Nguyen Phu Trong -- and President To Lam.

Reporters Without Borders ranks Vietnam 174th out of 180 countries and territories in its press freedom index. It says: "Vietnam's traditional media are closely controlled by the single party. Independent reporters and bloggers are often jailed, making Vietnam the world's third largest jailer of journalists."