A Vietnamese court has given lengthy jail sentences to 14 rights activists convicted of plotting to overthrow the communist government.

Following a brief two-day trial, the defendants received sentences Wednesday ranging from three to 13 years in prison. Another defendant was given three years of house arrest.

The court in the northern Vietnamese province of Nghe An ruled the activists had links to the banned opposition group Viet Tan, which is based in the United States and labeled by Hanoi as a terrorist organization.

In a statement, Viet Tan condemned what it called the “arbitrary conviction” of the activists, who it said have “tirelessly advocated for social justice, engaged in citizen journalism, and participated in peaceful demonstrations.”

The U.S. Embassy in Hanoi also said it was “deeply troubled” by the convictions. It called on the government to release the activists immediately, saying it is part of a “disturbing human rights trend in Vietnam.”

A defense attorney for the activists said Tuesday there was no evidence the accused are members of the California-based group, and said there were several violations in the prosecution process.

Viet Tan says it works with other pro-democracy groups inside and outside Vietnam to “overcome dictatorship and build the foundation for a sustainable democracy” through “peaceful, nonviolent struggle.”

It has neither confirmed nor denied that the 14 activists, who were detained in 2011, are among its members. Many of the activists were Catholic bloggers that rights groups say were exercising their rights to freedom of expression.