Five gay rights activists have been detained in Moscow as they tried to deliver a petition to the office of Russia's prosecutor general.
Police said they were held because their action was unauthorised.
The activists said more than two million people had signed the petition to investigate alleged torture and detentions of gay people in the Russian region of Chechnya.
Chechen officials have denied that gay people even exist in the republic.
Last week, Russian President Vladimir Putin backed an inquiry into the reported crackdown on gay people in Chechnya, in the North Caucasus.
Earlier this month German Chancellor Angela Merkel urged the Russian authorities to help protect gay rights.
On Thursday, four Russians and an Italian national were held as they tried to deliver a printout of the petition to the prosecutor general's office.
They also carried huge empty boxes, symbolising online signatures they had collected in protest against the alleged crackdown, a BBC Russian reporter says.
The petition was signed "by more than two million people around the world, more than the entire population of the Chechen republic," the Russian LGBT Network said.
It said they were demanding "an unbiased investigation of illegal detentions of hundreds of people in Chechnya because of their homosexuality".
Chechnya's strongman leader, Ramzan Kadyrov, said last week he was ready to co-operate with Russia's federal authorities on the issue.
But Mr Kadyrov repeated recent assertions that there were no "people of non-traditional orientation" (a term sometimes used to describe LGBT people in Russia) in the predominantly Muslim republic.
Chechen officials also say the local police have not received any official complaints from alleged victims.
'It's the extermination of gay men'
Just a few weeks ago, "Ruslan" was with his wife and children in Chechnya. Now he's in a safe house for men fleeing detention and torture for being gay.
Reports of a campaign against gay men by Chechen security forces have been trickling through since early April when they first appeared in a Russian newspaper. Now some of the alleged victims are starting to speak out.
"When they brought me in, I denied everything," says Ruslan - not his real name. Even now, he is frightened of being identified.
Homophobia is widespread in Chechnya. Last month, Natalia Poplevskaya of the Russian LGBT Network said there was "an organised campaign to detain gay men" in Chechnya.
Victims of the crackdown - who were either gay or just perceived to be gay - were being held at a detention centre near Argun, 20km (13 miles) from the city of Grozny, she said.
"Torture is going on with electric shocks, beatings with cables," she told the BBC, adding that three deaths had been reported. "All the people arrested are homosexual men or perceived as being gay."
A Chechen government spokesman, Alvi Karimov, denied the allegations. "You can't detain and repress people who simply don't exist in the republic," he said.
Homosexuality was decriminalised in the Russian Federation in 1993 but concern about homophobia remains high.
In 2013, parliament passed a law imposing heavy fines for providing information about homosexuality to people under 18, sparking international controversy.