MELEKHOVO, Russia Jailed opposition leader Alexei Navalny appeared before a Russian court on Monday to face new charges of extremism that could extend his prison term by decades.

The hearing took place at the IK-6 penal colony in Melekhovo, about 235 km (145 miles) east of Moscow, where Navalny is already serving sentences totalling 11-1/2 years.

His supporters accuse Russian authorities of trying to break him in prison to silence his criticism of President Vladimir Putin, something the Kremlin denies.

An entry in the court record last month showed the new charges relate to six different articles of the Russian criminal code, including inciting and financing extremist activity and creating an extremist organisation.

Russia has outlawed Navalny's campaign organisation as part of a crackdown on dissent that started well before the conflict in Ukraine and has intensified in the nearly 16 months since it started. Last week one of his regional campaign leaders was jailed for 7-1/2 years.

In a tweet posted on his account by his supporters last month, Navalny responded with typical irony to the new charges.

"Well, Alexei, you're in some real trouble now ... The Prosecutor General's Office has officially provided me with 3,828 pages describing all the crimes I've committed while already imprisoned."

He said he had not been allowed to read the material to find out what exactly he was accused of because he was once again in solitary confinement and allowed only a mug and one book.

Navalny, 46, earned admiration from the disparate opposition for voluntarily returning to Russia in 2021 from Germany, where he had been treated for what Western laboratory tests showed was an attempt to poison him with a Soviet-era nerve agent.

The Kremlin denied trying to kill him and said there was no evidence he had been poisoned with such a toxin.

It was not immediately clear which specific actions or incidents the new charges referred to.

One relates to "rehabilitation of Nazism" - a possible reference to Navalny's declarations of support for Ukraine, whose government Russia accuses of embodying Nazi ideology. Ukraine and its Western allies dismiss that charge as baseless.

In April, investigators formally linked Navalny supporters to the murder of Vladlen Tatarsky, a popular military blogger and supporter of Russia's military campaign in Ukraine who was killed by a bomb in St Petersburg.

Russia's National Anti-terrorism Committee (NAC) said Ukrainian intelligence had organised the bombing with help from Navalny's supporters.

This appeared to be a reference to the fact that a suspect arrested over the killing once registered to take part in an anti-Kremlin voting scheme promoted by Navalny's movement.

Navalny allies denied any connection to the killing. Ukraine attributed it to "domestic terrorism".

(Reporting by Reuters; writing by Mark Trevelyan; Editing by Kevin Liffey)