Russian police arrested at least 30 activists in central Moscow on Saturday at a gay pride rally to mark 20 years since homosexuality was decriminalised.

Police officers pounced on the gay campaigners moments after they unfurled banners and rainbow-coloured flags outside the State Duma, Russia's lower house of parliament, on Saturday afternoon. Several protesters were attacked by Orthodox Christian vigilantes. The arrests were made outside the Duma and the Moscow mayor's office where the rally ended. Activists chose to rally by the Duma to protest against a federal bill that would impose fines of up to 500,000 roubles (£10,500) for promoting homosexuality among minors. More than 10 regional legislatures across Russia have passed similar laws which have been widely condemned.

More than two decades after the fall of the Soviet Union, Russia remains deeply conservative and independent opinion polls show that about three-quarters of the population support suppressing public displays of homosexuality.

Officers patrolling outside the Duma shouted from megaphones: "Your rally is not sanctioned, you're disrupting passers-by" while police trucks fitted with metal cages waited nearby. Moscow authorities had refused permission for the rally for the eighth year in a row, saying it would interfere with students out celebrating the last day of term.

"I don't understand why police are hauling people away," said Gleb, an activist who was soon detained. "We're only asking for equal rights, the same as for everyone else."

Police also arrested several nationalists and Orthodox Christian believers, who sang hymns and crossed themselves as if to ward off evil spirits. "Gay people need medical treatment. It's simply disgusting to look at them," said Konstantin Kostin, a member of the Holy Rus movement. "Russia used to be a great superpower. Now look what's become of us. Marriage is a sacred union between man and woman, and this lot want to defile the sanctitude of our country."

The Orthodox Christian church, which enjoys pride of place among the country's many faiths, has stoked intolerance towards gays, describing homosexuality as a moral threat to Russia. Last week, Patriarch Kirill, Russia's top religious official, said his church would never recognise same-sex marriages.

Nikolai Alexeyev, an organiser of the rally and a leading gay rights campaigner, said in an interview on the eve of the rally that he had been forced to spend Friday night away from home in order to evade capture. He blamed President Vladimir Putin, who Alexeyev said has presented himself as a champion of traditional Russian values, since returning for a third term last year, and for discrimination against sexual minorities. In the Netherlands last month, Putin criticised same-sex couples for not contributing to Russia's flagging birthrate.

Alexeyev, who was also arrested, said: "Putin is personally responsible. If he gives the order to allow gay pride events, then people's perception of the gay community will radically change. In Russia, everything is done by the tsar's decree."

The gay pride rally comes weeks after the brutalised body of a 23-year-old man was found in Vologograd, southern Russia . The killing outraged the LGBT community, which says such attacks are on the rise.

Alexeyev, who was fined 5,000 roubles in St Petersburg a year ago for "homosexual propaganda", said Russian authorities continued to portray gay people as "freaks" to distract public attention from the government's wider failings.

With little to show for the past eight years of campaigning, he said activists now believe intolerance towards gay people could persist for many years to come. Alexeyev added: "When we started applying to hold gay pride events, I thought we'd make people listen, but now, I have my doubts."