A Russian court jailed a mathematician for six years on Monday for breaking a window at an office of President Vladimir Putin's ruling party, causing outrage among activists.

Azat Miftakhov was convicted of "hooliganism" his lawyer Svetlana Sidorkina told Agence France-Presse (AFP), adding that he would appeal the ruling.

"We don't agree with this decision ... based particularly on two anonymous witness statements that could not be verified," Sidorkina said.

Rights group Memorial has called Miftakhov a political prisoner and almost 90,000 people have signed a petition calling for his release.

More than 2,500 mathematicians from around the world have threatened to boycott a 2022 congress in Saint Petersburg if he is not freed, Russian newspaper Novaya Gazeta reported.

A doctoral student at Moscow State University, 27-year-old Miftakhov openly calls himself an anarchist activist.

He was arrested in February 2019, accused of belonging to a group of six people who a year earlier allegedly broke the window at a United Russia party office in northern Moscow and threw a smoke bomb inside.

He had previously been arrested on suspicion of manufacturing an explosive, although he has so far not been charged with that crime.

His lawyer said police officers hit him and pressured him while he was being held for the bomb-making offense.

In recent months, Russian authorities have sentenced several groups of young far-left supporters, some of them very harshly, in cases blasted by human rights defenders.