The United States has expressed alarm over prison terms handed down against three Vietnamese democracy activists for obstructing traffic.

Human rights groups have described the charges used to convict Bui Thi Minh Hang, Nguyen Thi Thuy Quynh and Nguyen Van Minh to 3 years, 2 years and 2 1/2 years respectively on Tuesday as "bogus."

The three were arrested earlier this year as they rode motorbikes to visit a former political prisoner in Dong Thap province.

The U.S. Embassy late Tuesday said "the use of public disorder laws by Vietnamese authorities to imprison government critics for peacefully expressing their political views is alarming."

Vietnam's human rights record complicates Washington's efforts to seek closer ties with the Southeast Asian nation, part of a push to counter Chinese influence in the region.

Scores of activists are imprisoned in Vietnam on charges relating to freedom of expression, and others complain of intimidation and violence. Human Rights Watch says that the number of people sentenced in political trials in Vietnam has increased every year since 2010, and that at least 63 people were imprisoned for peaceful political expression last year.

Vietnam's government has gradually opened up its economy to foreign investors and overseen a dramatic improvement in living standards over the last 20 years, but it remains a one-party state that doesn't allow basic political freedoms.