Russia's top human rights official has joined a campaign calling for two members of punk band Pussy Riot to be freed from jail.

Vladimir Lukin, the country's human rights commissioner, is backing an appeal against the hooliganism convictions and two-year prison sentences handed out to Nadezhda Tolokonnikova and Maria Alekhina last year (12).

The two rockers were among three members of the punk collective who were arrested for performing a protest song against President Vladimir Putin at a church in Moscow.

Their bandmate Yekaterina Samutsevich was freed in October (12) when her sentence was commuted, and now Lukin has joined the growing band of supporters backing Tolokonnikova and Alekhina's appeal, which is currently under consideration by officials at Russia's highest legal panel, the Moscow City Court Presidium.

According to a report published in Russian newspaper Kommersant, Lukin has written an entry in the appeal papers stating the pair only violated "the internal rules of conduct in the given cathedral" and that there is no proof they planned to cause religious offence.

The jail sentences sparked outrage last year, with stars including Sir Paul MCCartney, Madonna, and Bjork speaking out against the decision.