Russian authorities have opened a criminal case against four Jehovah’s Witnesses in Siberia, in the latest persecution against the religious group.

The Investigative Committee in the Tomsk region charged the four believers for participating in an extremist group, the human rights monitoring group OVD-Info and Jehovah’s Witnesses in Russia said on March 29.

The four were identified as Sergei Belousov, Andrei Kolesnichenko, Aleksei Ershov, and Andrei Ledyaykin.

The case was opened in Seversk, a closed city due to its nuclear and chemical facilities.

Russia labeled the Jehovah’s Witnesses an extremist group and banned it in 2017, leading to a wave of court cases and prison sentences against its members.

For decades, the Jehovah’s Witnesses have been viewed with suspicion in Russia, where the dominant Orthodox Church is championed by President Vladimir Putin.

The Christian group is known for door-to-door preaching, close Bible study, rejection of military service, and not celebrating national and religious holidays or birthdays.