HANOI, Vietnam (AP) — A court in Vietnam's Ho Chi Minh City on Tuesday began the trial of 12 people, including two American citizens, on subversion charges as government authorities step up a crackdown on dissent.

The official Vietnam News Agency said the defendants are accused of attempting to overthrow the government by recruiting members for a U.S.-based exile group called the Provisional Central Government of Vietnam and by engaging in anti-state activities.

Vietnam's government has labeled the little-known group a terrorist organization.

The news agency said two Vietnam-born American citizens are accused of ordering other members of the group to distribute anti-state leaflets, take over state radio stations to broadcast anti-government messages, and participate in anti-government protests. It said most of the plans were thwarted.

The news agency identified the Americans as Han James Nguyen and Angle Phan. It did not provide their hometowns.

The trial is scheduled to last three days.

"We are taking all appropriate actions to ensure Mr. Nguyen's welfare and to encourage an expeditious resolution to his case. Due to privacy concerns, we are unable to comment on any other case," a U.S. State Department official said in a statement.

In January, Vietnam's Ministry of Public Security declared the California-based group a terrorist organization, a month after 15 alleged members were convicted in a failed bombing at the country's largest airport.

The attempted attack at the Tan Son Nhat airport in Ho Chi Minh City in April last year caused a scare but no casualties.

Last week a court in central Vietnam sentenced an activist to 20 years in prison after finding him guilty of attempting to overthrow the government.

Despite sweeping economic reforms over the past 30 years that opened the country to foreign trade and investment and made Vietnam one of the world's fastest growing economies, the government tolerates no challenge to its one-party rule.

Amnesty International says 97 people are serving prison sentences for violating national security laws, while Human Rights Watch counts 119.