A group of Russian anti-gay activists sued American pop star Madonna for US$10 million (NZ$12.3 million) on Friday, saying she had insulted their feelings when she spoke out for gay rights at a concert in St Petersburg last week.

Performing in black lingerie with the words "No Fear" scrawled on her back, Madonna attacked a city law adopted in March that imposed fines for spreading homosexual "propaganda". She had earlier called the law a "ridiculous atrocity".

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

"She (Madonna) had been warned with words that she should behave in line with the law and she ignored it. So we will speak in the language of money," said Darya Dedova, one of the 10 activists who filed the lawsuit in a St Petersburg court.

"Of course, it is difficult to measure moral damages and suffering but maybe people who earn money regardless of moral rules will better understand this," Dedova said. She added if they won the case, the money would be sent to orphanages.

"Maybe someone does not see the link but after Madonna's concert maybe some boy becomes gay, some girl becomes lesbian, fewer children are born as a result and this big country cannot defend its borders - for me it causes moral suffering," said Alexei Kolotkov, another of the activists who filed the suit.

The St Petersburg propaganda law is the model for a bill that has been submitted to the national parliament but has not yet faced a vote. Critics say they fear it could be used to clamp down on the lesbian, gay, bisexual and transgender community, for example by barring gay rights demonstrations.

In Moscow, gay rights suffered a blow when an appeal court upheld a lower court's ruling that found city authorities had acted legally when they rejected applications from activists to hold a gay rights march every year for the next 100 years.

Attempts to hold gay rights rallies in the Russian capital have often ended in arrests and clashes with anti-gay activists.

In May, dozens of people were detained in Moscow after Russian Orthodox activists broke up two gay rights marches, throwing water and shouting prayers.

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