* Court finds six adherents guilty of extremism
* Men sentenced for up to three-and-a-half years
* Jehovah's Witnesses call move harsh and absurd
* Lawyers plan to appeal against the sentences (Updates with details, context)
By Andrew Osborn and Tom Balmforth
MOSCOW, Sept 20 (Reuters) - Russia has widened a crackdown against Jehovah's Witnesses, jailing six adherents of the Christian denomination for extremism in a move rights activists said was unjust and flouted religious freedom.
A regional court in Saratov jailed six Jehovah's Witnesses on Thursday for up to three-and-a-half years, a court spokeswoman said on Friday.
"Yes they were convicted," the spokeswoman, Olga Pirueva, said. "Punishments ranged from three years and six months down to two years (in jail)."
The court found the six men guilty of continuing the activities of an extremist organisation, a reference to a 2017 ruling from Russia's Supreme Court which found the group to be an "extremist" organisation and ordered it to disband.
The U.S.-headquartered 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.
The latest jailings follow the conviction in February of a Danish builder in Russia for his association with Jehovah's Witnesses. Dennis Christensen was found guilty of organising an extremist group and jailed for six years.
Over 250 Jehovah's Witnesses in Russia are facing criminal charges, according to the group, with 41 in detention and 23 under house arrest.
'SPECULATIVE THESIS'
Under Thursday's ruling, Konstantin Bazhenov and Alexei Budenchuk were sentenced to three-and-a-half years in jail, Felix Makhammadiev to three years, and Roman Gridasov, Gennady German, and Alexei Miretsky to two years in prison each.
The court also banned them from holding leadership positions in public organisations for five years.
Jehovah's Witnesses say Russia's constitution guarantees their adherents' right to exercise freedom of religion and deny wrongdoing.
"The whole logic of the accusation was based on the speculative thesis that faith in God is 'a continuation of the activities of an extremist organization'," Jarrod Lopes, a U.S.-based spokesman for the group, said in a statement.
"Instead of searching and proving the guilt of the defendants, the aim of the investigation was to prove their religious affiliation, despite the fact that no religion is prohibited in Russia."