(Bloomberg) -- Russian police in riot gear fired tear gas and stun grenades to violently break up a large protest in the central Bashkortostan region after a local activist was sentenced to four years in prison.

The clash with demonstrators came after several thousand people massed outside a courthouse in the town of Baymak to protest the jailing of Fail Alsynov on a charge of inciting hatred over a speech he made in April last year, local independent media reported. That speech concerned a plan to mine for gold in the majority-Muslim republic with the use of migrant workers.

The episode was one of the biggest instances of unrest since Russia’s invasion of Ukraine in February 2022, and comes as the number of local protests grows over issues such as environmental rights. The Kremlin has cracked down on critics of President Vladimir Putin since the war, imprisoning opponents or forcing them into exile.

Law enforcement officials opened a criminal case related to mass disturbances and assaults on police, according to a statement by the Investigative Committee. Investigators alleged that social networks were used to urge people to gather for the protest during a hearing in Alsynov’s case, according to the Interfax news service.

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