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More than 100 famous musicians including Madonna, Elton John and Sting called Monday for Russia to release two members of feminist punk-rock band Pussy Riot, jailed for an anti-government protest performance.

In an open letter coordinated by rights group Amnesty International, the celebrities voiced their support for Maria Alyokhina, 25, and Nadezhda Tolokonnikova, 23, and decried their "shockingly unjust trial and imprisonment."

The two women are being held in separate Russian penal colonies to serve two-year jail terms imposed after their band performed a protest song against President Vladimir Putin in an Orthodox cathedral in Moscow in February, 2012.

"While understanding the sensitivities of protesting in a place of worship, we ask that the Russian authorities review these harsh sentences, so that you may return to your children, your families and your lives," read the letter.

"You have been accused of what could be described as 'a victimless' crime, but in our opinion, in a just society, there can be no crime where there is no identifiable victim," it continued.

"Your strength, bravery and fearlessness are an inspiration to us all," concluded the letter, signed by the likes of Joan Baez, Bjork, the Clash, PJ Harvey, Patti Smith, Paul McCartney, Youssou N'Dour and Bruce Springsteen.

The letter was published ahead of scheduled appeal hearings on July 24 and 26 for the two imprisoned band members, nearly a year after their initial sentences last August.

A third member of the band, Yekaterina Samutsevich, was convicted but later released on appeal with a suspended sentence and strict probation conditions.