ST. PETERSBURG, Russia -- Two Russian activists from a group known as Set (Network) have received lengthy prison terms on charges of being members of a terrorist group that planned to overthrow the country's authorities.

On June 22, the Second West Territory's Military Court sentenced Viktor Filinkov to 7 years and Yury Boyarshinov to 5 1/2 years in prison in a case opposition figures and rights defenders have called "fabricated."

Filinkov's lawyer, Yevgenia Kulakova, announced that the defense would appeal the verdict, which sparked protests near the courthouse.

Several dozen people gathered there chanting slogans such as “Shame!” and “Freedom for political prisoners.”

A total of 30 participants were detained by police, according to OVD-Info, an independent political watchdog.

Before the trial resumed its final session, police detained a young man who had handcuffed himself to the court's fence, ignited a firecracker, and chanted: "Let them go!" and "FSB [Federal Security Service] is the main terrorist!"

The man also scattered pieces of paper with the word "Liberty!" written on them.

Filinkov and Boyarshinov went on trial in late February.

Boyarshinov had pleaded guilty, saying that he did not know that Network was a terrorist group when he joined it. Filinkov rejected the charges, saying that his initial guilty plea was given under duress.

Russian investigators said the group planned to organize a series of explosions in Russia during the presidential election and the World Cup soccer tournament in 2018 "to destabilize the situation" in the country and to organize an armed mutiny.

Rights activists have said the charges are false, while some of those arrested have claimed they were tortured while in custody. The Investigative Committee has rejected the claims.

In February, a court in another Russian city, Penza, sentenced seven other activists of the group to prison terms of between six years and 18 years after convicting them of terrorism.

The group members were arrested in October 2017 for allegedly creating a terrorist group with cells in Moscow, St. Petersburg, Penza, and Omsk, as well as in neighboring Belarus.

Belarusian authorities told RFE/RL in February that they weren’t aware of a Network cell existing in Belarus.

Amnesty International has called the terror charges "a figment of the Russian security services' imagination...fabricated in an attempt to silence these activists."

The London-based human rights watchdog maintains the case is “the latest politically motivated abuse of the justice system to target young people.”

Two other activists initially arrested in the case, Igor Shishkin and Yegor Zorin, made deals with investigators and testified against the others.

Shishkin received 3 1/2 years in prison in January 2019, while the case against Zorin was closed in September 2018.

With reporting by AP