A Vietnamese court sentenced three high-profile bloggers to jail terms ranging from four to 12 years on Monday, in the latest crackdown on dissent as booming Internet usage threatens to undermine the Communist government's authority, Reuters reported.

Bloggers in Vietnam, which has one of the world's fastest growing Internet populations, have grown bolder in criticizing the government over issues ranging from land rights to corruption, and China's growing regional influence.

That comes as Vietnam's economy, not long ago a star of Southeast Asia, faces a slowdown in the wake of debt scandals at its huge state enterprises that have undermined investor confidence and exposed divisions in the Communist leadership.

The government has responded to the growing dissent with a crackdown that has earned it the title of "Enemy of the Internet" from media freedom group Reporters Without Borders, which says only China and Iran jail more journalists.

Nguyen Van Hai, who criticized government policies under his blogging name Dieu Cay, was jailed for 12 years for "anti-state propaganda", according to a lawyer for the bloggers who attended the brief trial in southern Ho Chi Minh City on Monday.

Fellow bloggers Ta Phong Tan and Phan Thanh Hai got 10 years and four years respectively, said the lawyer, Ha Huy Son. All three were founding members of the Free Journalists Club, a website set up for bloggers to post their writing.

The U.S. embassy in Hanoi said in a statement it was "deeply concerned" by the verdict, which it said appeared to contradict Vietnam's international human rights commitments, and called for their release.