An apparent homophobic killing has increased concerns among Russian activists about prejudice against gays, which they fear will be encouraged by a bill banning homosexual "propaganda".
The body of a 23-year-old man was found in the courtyard of an apartment building in the southern city of Volgograd early on Friday with multiple wounds including in the genital area, the federal Investigative Committee said on Saturday.
It said a 22-year-old acquaintance of the victim and a 27-year-old ex-convict had been detained on suspicion of murder.
A investigator in Volgograd, Andrei Gapchenko, told Ekho Moskvy radio that the suspects said they had been drinking with the victim and began beating him after he told them he was gay.
It is rare for law enforcement authorities in Russia to specify suspicions that homophobia was the motive in an attack, and activists say many attacks against gays are not treated or described as such by the police.
Prominent gay rights activist Nikolai Alexeyev said a bill to outlaw spreading "homosexual propaganda" among minors, given preliminary approval by parliament in January, would make Russians less likely to fear consequences for attacking gays.
"This monstrous incident in Volgograd demonstrates the fruits of the homophobic policy that is being conducted in this country, including the initiative to ban homosexual propaganda," Interfax news agency quoted Alexeyev as saying.
Critics say the bill, expected to win final parliamentary approval within weeks, would effectively ban gay rights demonstrations and sharply curb basic freedoms.
Some members of United Russia, the party that is loyal to Putin and dominates parliament, want to add a clause that would levy fines for any public support for homosexuality.
President Vladimir Putin has often championed socially conservative values since he began a third term last May.
Met by protests against the legislation on a trip to the Netherlands last month, Putin denied his government discriminates against gays, but criticised them for failing to aid population growth.
The United States has criticised the bill and Russian rights activists say it is part of an effort by Putin to appeal to conservative voters after months of protests by mostly liberal Russians tired of his 13-year dominance.