DUSHANBE -- Tajik opposition activist Hizbullo Shovalizoda, who was extradited from Austria in March, has been sentenced to 20 years in prison on extremism charges.

Shovalizoda's relatives told RFE/RL on June 12 that the activist was sentenced two days earlier after being found guilty on charges that included participating in the activities of an extremist organization and high treason.

Supreme Court officials refused to comment on Shovalizoda's trial, saying that the case was classified.

Shovalizoda's father, Abdullo Shovalizoda, told RFE/RL that no family member was invited to the trial.

"We do not even know the specific details of the charges," Abdullo Shovalizoda said.

Austrian authorities extradited 29-year-old Shovalizoda to Dushanbe in early March.

Tajik authorities said at the time that Shovalizoda was suspected of being a member of the banned Islamic Renaissance Party of Tajikistan (IRPT) and participating in an attempt to overthrow the government by force.

The IRPT, long an influential party with representatives in the government and parliament, was labeled a terrorist group and banned in 2015.

Dozens of IRPT officials and supporters have been prosecuted and many of them imprisoned, drawing criticism from human rights groups.

Shovalizoda arrived in Austria more than a year ago and asked for asylum, but instead was placed under arrest in January.

Tajik opposition activists in exile told RFE/RL that they had urged the Austrian authorities not to extradite Shovalizoda, as he was not a member of any political opposition group or party.

The IRPT said at the time that Shovalizoda had never been a member.

"Shovalizoda is most likely to be subjected to torture, ill-treatment, and unfair trial. He, as in previous similar situations, may be forced to testify against himself and other people under torture," the party said in a statement at the time.

Tajik authorities have been criticized for cracking down on dissent for years.

In 2014, the opposition movement Group 24 was labeled as terrorist and extremist and banned. In March 2015, the movement's founder, Umarali Quvatov, was assassinated in Istanbul, Turkey.