Twenty years after homosexuality was decriminalised in Russia, anti-gay legislation is making a rapid comeback, with St Petersburg becoming the latest city to ban "homosexual propaganda".

The law, signed by St Petersburg's governor last week, came amid increasing calls by leading Russian politicians and Orthodox Church officials to bring anti-gay laws to the federal level. Dmitry Pershin, head of the Church's youth council, renewed those calls on Mondayafter praising the St Petersburg law for "helping to protect children from information manipulation by minorities that promote sodomy".

The law's content is vague – it criminalises "public action aimed at propagandising sodomy, lesbianism, bisexualism, and transgenderism among minors". Those charged with breaking the law will be fined from 5,000 (£108) to 500,000 roubles.

Gay rights activists say the law is part of a wider government initiative, supported by the strictly conservative Orthodox Church, to crack down on public protest, civic activity and the liberalisation of society.

"The tendency in Russia is toward limiting freedom of speech and freedom to gather, targeting any group that somehow stands up for its rights," said Yury Gavrikov, the head of Equality, one of several gay rights groups in St Petersburg.

"No one knows how the law will work," Gavrikov said. "The main goal seems to be limiting the rights of those who engage in social activity. But in its widest sense, it can mean limiting exhibits, plays, film showings – cultural activities."

After Ryazan, Arkhangelsk and Kostroma, St Petersburg is the fourth city to pass such a law. Its adoption in Russia's most European city and one with a relatively vibrant gay scene has sparked an international outcry. All Out, a global gay rights group, has called on people to avoid travelling to the city until the law is repealed.

St Petersburg's governor, Georgy Poltavchenko, signed the law on 7 March, his office said on Sunday. It is due to come into force within 10 days.

Nikolai Alexeyev, Russia's most outspoken gay rights activist, said he would launch a protest campaign to get the law repealed. He has also sued the law's initiator, St Petersburg United Russia deputy, Vitaly Milonov, for 1m roubles after the politician called him a girl who supported himself on western grants.

Soviet-era laws that criminalised homosexuality were repealed in 1993, but anti-gay sentiment remains widespread in Russia. The St Petersburg law includes amendments introducing stricter punishment for paedophilia, which is commonly conflated with homosexuality.

A Levada Centre poll released in July 2010 found that 38% of Russians thought homosexuality was a "bad habit" and 36% thought it was "a sickness or result of a psychological trauma". Yet the same poll found that 41% supported laws banning discrimination based on sexual orientation, while 31% were against it and the rest were undecided.

Church officials and close allies of the president-elect, Vladimir Putin, including the former governor of St Petersburg and head of Russia's Federation Council, Valentina Matviyenko, support the establishment of national anti-gay laws.

Gay pride parades are regularly banned in Russia and violently broken up by police. Milonov once called gays "perverts", while the former Moscow mayor Yury Luzhkov regularly compared homosexuality to Satanism.

"Today, our government's politics are rather authoritarian in character," said Gavrikov. "The thoughts of minorities – even political minorities – are never taken into account. What matters is what the party and its leadership, as embodied by Vladimir Putin, thinks."