A court in Vietnam has sentenced two Americans to 14 years in jail for to “attempting to overthrow the state”, state media reported.

James Nguyen and Angle Phan were accused of plotting to hijack radio stations to broadcast anti-state messaging and of arranging anti-state protests, as members of the California-based Provisional National Government of Vietnam.

The pair had apparently been brought over from the US to “develop their force and direct other members in the country to conduct anti-state activities.”

The previously unknown group had been declared a terrorist organisation by the Vietnamese government in January after 15 of its members were charged with an alleged failed plot to blow up the airport in Ho Chi Minh City.

In this week’s trial, which lasted two days, 10 members of the group were convicted, including Nguyen and Angle – who are Americans of Vietnamese descent. They will be deported from Vietnam after the completion of their 14 year-jail terms.

According to the state news agency, the judge said the defendant’s acts were “particularly serious, violating national security, sabotaging the country’s stability and development, causing instability in political and social order and going against the interests of the state.”

In a statement, the US embassy said: “We will continue to monitor Mr Nguyen’s welfare, advocate for him and provide consular services until his release.” A spokesperson for the embassy said it was not authorised to speak on behalf of Phan.

Vietnam regularly jails bloggers, activists and anyone seen to be promoting anti-government messaging, but the crackdown has increased in recent months. In response to a rare street protest last month, when hundreds took to the streets to voice anger at growing Chinese influence in the country, the government jailed dozens who took part.

The Provisional Central Government of Vietnam organisation was formed in the 1990s by former soldiers who fought on the side of the US-sponsored south Vietnam, the side which lost in the Vietnam war.

The group is dedicated to bringing about “free and fair elections in Vietnam” and “to unify all the hope and desire of the freedom-loving Vietnamese to become a National Resolution to discharge the dictatorship of communist in Vietnam,” according to their website.

Reuters contributed to this report