A Russian climate youth activist has been sentenced to six days in prison for taking part in a demonstration in Moscow.

Supporters said the punishment of Arshak Makichyan was disproportionately severe, and was one of the harshest crackdowns on student campaigners anywhere in the world.

Makichyan, a 25-year-old violinist, was inspired by Greta Thunberg to join the Fridays for Future movement, which urges governments to listen to scientists and meet the commitments they made in the Paris agreement.

He had recently returned from international climate talks in Madrid but was summoned by the Russian authorities on Friday to face charges that he participated in a protest without permission.

Earlier, he tweeted thanks to his lawyer and supporters. “We are waiting for the judge’s decision,” he wrote, then later updated with the verdict: “Six days of arrest.”

Climate activists from dozens of other countries expressed solidarity on social networks. “Hang in there. You are doing the right thing,” said the Fridays4Future Twitter account, which described the activist as an inspiration.

You are an inspiration to many activists out there Arshak. Hang in there. You are doing the right thing ✊🏽💚

/FFF Twitter team — FridaysForFuture (@Fridays4future) December 20, 2019

Makichyan had been staging a solo school strike in Pushkin Square, Moscow, for more than 40 weeks. Under Russia’s tight restrictions on gatherings, individual protests are lawful but anything bigger requires police permission.

Shortly before September’s global strike, Makichyan told the Guardian the lengths he and fellow Russian campaigners went to try to avoid problems with the authorities.

“In Moscow it is almost impossible to get permission for a mass demonstration so we protest in a queue. One person holds a poster for five minutes, then hands over to the next person who is waiting nearby. That way, we don’t have any problems because it is a series of solo strikes rather than a group gathering,” said the graduate of the Moscow Conservatory.