A Russian court has found a Danish Jehovah’s Witness guilty of organising a banned extremist group and jailed him for six years in a case raising fears of a return to Soviet-era religious persecution.

Armed police detained Dennis Christensen, a 46-year-old builder, in May 2017 at a prayer meeting in Oryol, about 200 miles (320km) south of Moscow following the banning of the local Jehovah’s Witnesses by a court a year earlier.

Russia’s supreme court later ruled the group was “extremist” and ordered it to disband nationwide. Christensen’s detention, Russia’s first extremism-related arrest of a Jehovah’s Witness, foreshadowed dozens more.

The court, in the city of Oryol, found Christensen guilty on Wednesday after a long trial, his lawyer, his wife and a representative for the Jehovah’s Witnesses told Reuters.

Christensen had pleaded innocent, saying he was exercising freedom of religion guaranteed in Russia’s constitution.

The Danish foreign minister, Anders Samuelsen, called on Moscow to respect religious freedom and criticised it for classifying Jehovah’s Witnesses on a par with terrorist groups.

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

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

They believe the end of the world as we know it is imminent, an event “the obedient” will survive to inhabit the kingdom of God they believe will follow.

Christensen moved to Murmansk, in northern Russia, where the Jehovah’s Witnesses were already well established, in 2000 and met his wife, Irina, there. The couple later moved to Oryol.

He speaks Russian and says he is a fan of Russian culture.

Anton Bogdanov, Christensen’s lawyer, said he planned to appeal against Wednesday’s verdict, which he said was illegal and which he feared would set a dangerous precedent.

More than 100 criminal cases have been opened against Jehovah’s Witnesses, with another 24 people in prison awaiting or on trial and a similar number under house arrest. Some of their publications are on a list of banned literature.

Yaroslav Sivulsky, a representative of the European Association of Jehovah’s Witnesses, said the verdict evoked the atheist Soviet period when Moscow persecuted the group.

“In essence we have returned to Soviet times,” said Sivulsky, whose own father, Pavel, was jailed for seven years in 1959 for printing Bible literature. “It’s sad that in the 21st century people are being jailed for holding what the authorities believe to be the wrong beliefs.”

Dmitry Peskov, a Kremlin spokesman, said there were clearly reasons for Christensen’s arrest but he was unaware of details.

Irina, Christensen’s wife, said she and her husband were calm despite what they saw as an injustice. Before the verdict, she said state TV had nurtured existing widespread prejudice in Russian society against Jehovah’s Witnesses, a strategy she said helped distract people from low living standards.