A court in Russia-annexed Crimea sentenced a Jehovah's Witness to six years in prison for extremism, the group said Thursday as Moscow pursues a crackdown on the US-based movement.

Russia outlawed the Jehovah's Witnesses in 2017, labelling them an extremist organisation. 

A court in Dzhankoy in the north of the Crimean peninsula sentenced Sergei Filatov, a 47-year-old father of four, to six years in prison, the religious group said.

"He is the first one of Jehovah's Witnesses in Crimea to be convicted for so-called extremist activity," said Jarrod Lopes, a New York-based spokesman for the religious movement.

"This bleak development in Crimea is the latest example of Russia exporting its patently extreme religious intolerance."

The Dzhankoy district court confirmed in a statement that it had sentenced a Jehovah's Witness to six years in prison.

The Jehovah's Witnesses said Filatov's home was searched in November 2018 in one of the largest special operations against the movement in recent years.

More than 35 law enforcement officers including heavily armed special forces raided his home, the group said, noting that two of his children are minors.

The group said the case was "rife with falsifications".

Moscow unleashed the crackdown on the Christian evangelical movement even though President Vladimir Putin said last year that Jehovah's Witnesses should not be considered terrorists.

Ten members have received prison terms in Russia since 2017, including in Crimea, which Moscow annexed from Ukraine in 2014.

Founded in the United States in the late 19th century, the movement has been repeatedly accused of proselytising or refusing to respect state symbols such as flags.