The jailed Russian opposition leader Alexei Navalny is facing a new trial on charges of extremism that could keep him in prison for decades.

Mr Navalny is already serving a nine-year sentence for parole violations, fraud and contempt of court.

He and his supporters insist his arrest and imprisonment in 2021 was politically motivated.

The latest trial will begin on Monday in the penal colony where he is being held, 250km (150 miles) east of Moscow.

Mr Navalny is facing multiple charges, including creating an extremist network and financing extremist activity.

He has said that could extend his prison term by up to 30 years.

A charismatic campaigner, he seemed to be the only Russian opposition leader capable of mobilising people in large numbers across Russia to take part in anti-government protests.

He was arrested in 2021 upon returning from Germany, where he recovered from a poison attack the previous year that he blamed on the Kremlin. The Russian authorities denied any involvement.

In 2020, a report by the investigative outlet Bellingcat and Russian news site The Insider implicated several agents of Russia's internal security service, the FSB, in the attack.

He was initially jailed for two and a half years for breaking bail conditions while being treated in a German hospital, but was then given an extra nine years for fraud and contempt of court.

The latest case comes as the Kremlin intensifies its crackdown on opponents, more than a year after invading Ukraine, with most key opposition figures behind bars or in exile.

Mr Navalny said that prosecutors provided him with 3,828 pages outlining all the crimes he is alleged to have committed while behind bars.

"Although it is clear from the size of the tomes that I am a sophisticated and persistent criminal, it is impossible to find out what exactly I am accused of," Mr Navalny said.

He has been charged with financing extremist activity, publicly inciting extremist activities and "rehabilitating the Nazi ideology", among other crimes.