Five Jehovah's Witnesses have been detained in Russia and charged with possessing weapons and running an extremist group, investigators said Wednesday, in the latest case targeting the banned religious movement.

They were arrested in the Kirov region northeast of Moscow, where authorities said they found two grenades and a landmine in searches of their homes.

The Jehovah's Witnesses are a Christian denomination that originated in the United States in the late 19th century.

The Russian authorities consider the movement a totalitarian sect and last year the country's supreme court banned the Jehovah's Witnesses from operating in Russia.

"They had been conducting meetings and called on others to join their organisation," Yevgenia Vorozhtsova, a spokeswoman for regional investigators, told AFP.

She said officials were investigating how the members of the Jehovah's Witnesses had obtained the ammunition, but declined to provide further details.

Yaroslav Sivulskiy, a member of the European Association of Jehovah's Christian Witnesses, said it was the first time the Russian authorities had accused members of the movement of possessing ammunition.

"We were shocked," he told AFP from the Latvian capital Riga. "It is both funny and strange. Why mines?"

One of those detained was a Polish national residing in Russia, he said.

- Searches in Smolensk region -

In a statement on Tuesday, investigators said the members of the Jehovah's Witnesses wanted the movement to continue operating in Kirov and nearby towns.

Authorities said they had organised clandestine meetings between August 2017 and September this year at which they sang hymns and read "extremist" literature banned in Russia.

They had also collected more than 500,000 rubles ($7,500) in donations from supporters.

The five have been detained and charged on suspicion of running and financing an "extremist organisation", the statement said.

Sivulskiy said the crackdown on Jehovah's Witnesses in Russia had intensified after President Vladimir Putin was re-elected for a fourth term in March.

Around 25 of their members are now in pre-trial detention in Russia, he said.

On Sunday, the FSB security service and police searched the homes of people they suspect of being members of The Jehovah's Witnesses in the western Smolensk region, the association said.

Two women from the town of Sychyovka have been incommunicado for the past three days, it said in a statement sent to AFP.

"They are thought to have been arrested," the statement said.

The FSB in Smolensk could not immediately provide a comment.

In a report this year, Human Rights Watch accused the Russian authorities of a "sweeping campaign" of harassment and persecution against the movement.

The Jehovah's Witnesses say they now number more than 170,000 in Russia, a country of 144 million people where most are Orthodox Christians. Thousands more of their members have fled to other countries.