MOSCOW (Reuters) - A Russian court jailed a Jehovah’s Witness adherent for six years on Friday after finding him guilty of extremist activity, part of a crackdown on the group that human rights activists say violates religious freedom.

A court in Penza, around 350 miles (563 km) southeast of Moscow, said in a statement it had jailed Vladimir Alushkin, 55, after an investigation had shown he was continuing to run a local branch of the U.S.-headquartered Christian denomination despite the group being outlawed as extremist in Russia.

It said it had also handed suspended two-year prison sentences to five other adherents.

Jehovah’s Witnesses have been under pressure for years in Russia, where the dominant Orthodox Church is championed by President Vladimir Putin. Orthodox scholars have cast them as a dangerous foreign sect that erodes state institutions and traditional values, allegations they reject.

“Vladimir’s six-year prison sentence is one of the harshest imposed on one of Jehovah’s Witnesses since the 2017 ban,” said Jarrod Lopes, a spokesman for the group.

“Russian authorities have remained obstinate in the face of repeated criticism from prominent international bodies and human rights advocates. The current state of religious freedom in Russia is reminiscent of Soviet times.”

Russia’s Supreme Court ruled in 2017 that the group was an “extremist” organization and ordered it to disband, a decision that was followed by a crackdown which has seen dozens of adherents detained and hundreds hit with criminal charges.

Alushkin was detained in July last year after what Lopes said was a raid on his home conducted by a dozen masked police officers with assault rifles.

Jehovah’s Witnesses say Russia’s constitution guarantees their right to exercise freedom of religion and deny wrongdoing.

President Vladimir Putin said last year he did not understand why authorities were pursuing the group and called for the matter to be analyzed. But the Kremlin has said since that the group remains illegal under current legislation and has declined to confirm whether the law will be changed or not.

Jehovah’s Witnesses are a Christian denomination known for door-to-door preaching, close Bible study, and rejection of military service and blood transfusions. The group has about 170,000 followers in Russia, and 8 million worldwide.

Rachel Denber of New York-based Human Rights Watch called on Russian authorities to halt its crackdown on the group.

“Alushkin and the others have done nothing wrong. They have the right to freedom of worship,” Denber wrote on social media after his sentencing. “Russia should reverse the ‘extremist’ designation against Jehovah’s Witnesses. And drop charges against all and free those in custody.”