Calling the legislation, which imposes fines for promoting homosexuality among minors, a "ridiculous atrocity" on her Facebook page, she said she would address the issue during her show.

"I will come to St Petersburg to speak up for the gay community, to support the gay community," she said. Her Russian tour begins in August, months after the Moscow opening of her private gym named after the artist's 2008 album "Hard Candy".

Homosexuality, punished with jail terms in the Soviet Union, was only decriminalised in Russia in 1993, but much of the homosexual community remains largely underground as anti-gay prejudice runs deep.

The legislation was signed into law in March by St. Petersburg mayor and Putin-ally Georgy Poltavchenko.

It imposes a fine of up to 500,000 roubles ($17,100) for spreading what the bill calls homosexual "propaganda" that could "damage the health, moral and spiritual development of the underaged", defined as those under the age of 18.

The law has caused concerns among the gay community that it could be used to clamp down on Russia's rare public displays of homosexuality, such as gay parades.

Gay rights activists in Moscow and St. Petersburg, have scheduled two "Slavic gay parades" during Madonna's tour according to the lesbian, gay, bisexual and transgender website GayRussia.eu.

Numerous attempts to hold gay protests in Moscow, ruled illegal by the authorities, have ended in multiple arrests and clashes with ultra-Orthodox believers who say homosexuals should be punished or treated in hospital for "illness".

In 2010 the European Court of Human Rights fined Russia for banning homosexual parades in Moscow, in what gay rights activists described as a historic victory.

Madonna sparked protests by Russian Orthodox church activists on a visit to Moscow in 2006, when she sang "Live to Tell" on a crucifix while wearing a crown of thorns. ($1 = 29.2875 Russian roubles) (Reporting By Nastassia Astrasheuskaya, Editing by Thomas Grove and Paul Casciato)

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