By Gabriela Baczynska

MOSCOW, Jan 25 (Reuters) - Russian police detained 20 people on Friday when gay activists tried to stage a "kiss-in" outside parliament to protest against a draft law banning the promotion of homosexuality among minors.

Police hauled away the protesters shortly before the lower house, the State Duma, was due to hold the first of three readings of the legislation, witnesses said.

Supporters of the law, some of them identifying themselves as Russian Orthodox Christians, cheered as the police stepped in and threw eggs at the protesters. Police confirmed that 20 people had been detained.

If approved by the two houses of parliament, and signed by President Vladimir Putin, the law would ban the promotion of gay events across Russia and impose fines on the organisers.

Putin's critics say it is the latest in a series of moves to appeal to conservative voters and consolidate support for him since his return to the presidency last May after a wave of protests against him in cities such as Moscow and St Petersburg.

Gay rights activists and human rights campaigners say the main aim of the law is not to protect children but to curb the rights of homosexuals.

"Animosity towards gays and lesbians is widespread in society, and the Duma, which has approved a number of unpopular laws, hopes it can win some popularity with an anti-gay law," veteran rights campaigner Lyudmila Alexeyeva told Reuters.

Supporters of the law say it is needed to prevent gay parades and television and radio programmes that support gay couples, describing this as homosexual propaganda which affects the development of children in Russia. (Writing by Gabriela Baczynska, Editing by Timothy Heritage)

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  • A supporter of a bill banning " homosexual propaganda" tries to grab a poster from the hands of a gay rights activist, during a protest near the State Duma, Russia's lower parliament chamber, in Moscow, Russia, Friday, Jan. 25, 2013. A controversial bill banning "homosexual propaganda" has been submitted to Russia's lower house of parliament for the first of three hearings on Friday, Jan. 25, 2013. The poster reads: I'm Blind and I'm Gay and I Refuse to be Invisible. P.S. Love is Stronger Then Hate. (AP Photo/Mikhail Metzel)

  • Police detain supporters of a bill banning "homosexual propaganda" near the State Duma, Russia's lower parliament chamber, in Moscow, Russia, Friday, Jan. 25, 2013. A controversial bill banning "homosexual propaganda" has been submitted to Russia's lower house of parliament for the first of three hearings on Friday. Twenty people were detained according to a police report. (AP Photo/Mikhail Metzel)

  • Police detain a gay rights activist during a protest near the State Duma, Russia's lower parliament chamber, in Moscow, Russia, Friday, Jan. 25, 2013. A controversial bill banning "homosexual propaganda" has been submitted to Russia's lower house of parliament for the first of three hearings on Friday. Twenty people were detained according to a police report. (AP Photo/Mikhail Metzel)

  • Police detain a gay rights activist during a protest near the State Duma, Russia's lower parliament chamber, in Moscow, Russia, Friday, Jan. 25, 2013. A controversial bill banning "homosexual propaganda" has been submitted to Russia's lower house of parliament for the first of three hearings on Friday. Twenty people were detained according to a police report. (AP Photo/Mikhail Metzel)

  • Gay rights activists protest near the State Duma, Russia's lower parliament chamber, in Moscow, Russia, Friday, Jan. 25, 2013. A controversial bill banning "homosexual propaganda" has been submitted to Russia's lower house of parliament for the first of three hearings on Friday. (AP Photo/Mikhail Metzel)

  • A gay rights activist holds a banner during a protest near the State Duma, Russia's lower parliament chamber, in Moscow, Russia, Friday, Jan. 25, 2013. A controversial bill banning "homosexual propaganda" has been submitted to Russia's lower house of parliament for the first of three hearings on Friday. The poster reads: I'm Blind and I'm Gay and I Refuse to be Invisible. P.S. Love is Stronger Then Hate. (AP Photo/Mikhail Metzel)

  • Police officers detain one of the gay rights activists during their protest just outside the lower house of Russia’s parliament, the State Duma, in Moscow, on January 25, 2013. Russia's parliament debated today a bill banning homosexual 'propaganda' among minors that could lead to gays being fined for demonstrating or kissing in public. AFP PHOTO / ANDREY SMIRNOV (Photo credit should read ANDREY SMIRNOV/AFP/Getty Images)

  • Police officers detain one of the gay rights activists during their protest just outside the lower house of Russia’s parliament, the State Duma, in Moscow, on January 25, 2013. Russia's parliament debated today a bill banning homosexual 'propaganda' among minors that could lead to gays being fined for demonstrating or kissing in public. AFP PHOTO / ANDREY SMIRNOV (Photo credit should read ANDREY SMIRNOV/AFP/Getty Images)

  • Police detain a gay rights activist during a protest near the State Duma, Russia's lower parliament chamber, in Moscow, Russia, Friday, Jan. 25, 2013. A controversial bill banning "homosexual propaganda" has been submitted to Russia's lower house of parliament for the first of three hearings on Friday. Twenty people were detained according to a police report. (AP Photo/Mikhail Metzel)

  • Gay rights activists protest near the State Duma, Russia's lower parliament chamber, in Moscow, Russia, Friday, Jan. 25, 2013. A controversial bill banning "homosexual propaganda" has been submitted to Russia's lower house of parliament for the first of three hearings on Friday. (AP Photo/Mikhail Metzel)