They confirmed that Dadin — who was jailed for 2.5 years under the law — had been a "peaceful" protester.

Judges ruled on Wednesday that while the law was legal under the Russian constitution, it should only be used against protesters who "posed a threat" to Russian society.

Dadin was the first Russian to be convicted under controversial new anti-protest laws in November 2015. The legislation prosecutes demonstrators who "repeatedly" hold unsanctioned protests, effectively outlawing public dissent which has not been pre-approved by the Russian government.

Dadin has not confirmed whether he will seek compensation for the time he has already spent behind bars.

In an interview with Russia's Dozhd television channel, Dadin's wife, Anastasia Zotova, said that she hoped the couple would leave Russia. "I'm scared that they will free him and arrest him again the next day," she said. "I don't want any more [of this.]"

The activist has also accused Russian prison guards of torturing him during his sentence at a prison camp in northern Russia.

In a letter addressed to his wife, Dadin alleged he was hung by his handcuffed wrists, threatened with rape and death, and beaten by a dozen guards at once.

The allegations sparked an investigations by Presidential Council on Human Rights and the Federal Penitentiary Service. The prison service said it found no evidence that Dadin had been beaten, but transferred the activist to a remote institution in Russia's Far East.