"It is crucial that reports of abductions, unlawful detentions, torture, beatings and killings of men perceived to be gay or bisexual are investigated thoroughly," the experts said in a statement posted on the website for the Office of the United Nations High Commissioner for Human Rights (OHCHR).
Since March, there have been increasing numbers of reports of gay men disappearing in Chechnya, according to a human rights activist and a leading opposition newspaper in Russia. Some are being detained; the fate of others is unknown, human rights groups say.
The newspaper, Novaya Gazeta, reported earlier this month
that the men were detained "in connection with their non-traditional sexual orientation, or suspicion of such," citing Russian federal law enforcement officials.
Novaya Gazeta reported that more than 100 gay men had been detained in two weeks in March and said it had the names of three who had been murdered.
CNN has not been able to independently confirm the newspaper's reporting. But Ekaterina Sokirianskaia, Russia project director of the International Crisis Group
, told CNN April 4 that in the previous 10 days she had received information from multiple sources in Chechnya about the detention of gay men, including a hairdresser and cultural and religious figures.
Sokirianskaia, a Moscow-based expert on the Caucasus region that includes the republic of Chechnya, said the volume of information made it "almost impossible to believe this is not happening, but it is also very difficult to verify because Chechen society is extremely homophobic."
She said it was unclear what had triggered the apparent anti-gay campaign.
'An April Fool's joke'
Russian President Vladimir Putin's spokesman, Dmitry Peskov, told reporters in a conference call Friday the Kremlin has no legitimate information on any such problems in Chechnya.
"We are unaware of any reports to the police or any complaints filed to them from the representatives of non-traditional sexual orientation regarding this. Maybe I'm mistaken and maybe some reports took place, but at least I haven't read anything about it. This information has to get verified," Peskov said.
He added that he was not aware of any investigation under way by Russian police about the alleged disappearances or detentions.
"If any citizens have their rights violated, those citizens normally complain to police -- they act according to the methods, suggested by the law," Peskov said.
The response from Chechnya -- an almost entirely Muslim republic, which includes part of Russia's border with Georgia -- was very different. The press secretary of the republic's Interior Ministry, Magomed Deniev, told Russian media April 3 that the report "is probably an April Fool's joke."
A spokesman for the Chechen government, Alvi Karimov, told the Russian news agency Interfax that the story in Novaya Gazeta was "an absolute lie."
But Karimov's fuller explanation underlined the deeply conservative and intolerant views of the republic's leadership.
"You can't detain and harass someone who doesn't exist in the republic," he said.
"If there were such people in the Chechen republic, law enforcement wouldn't have a problem with them because their relatives would send them to a place of no return."
Karimov appears to have been talking about so-called "honor killings" or the murders -- by their own family members -- of people who offended social conventions.
'Climate of fear'
Sokirianskaia at the International Crisis Group said honor killings still take place in Chechnya, and gay men would get no protection from their families, who would see them as a source of shame.
But she said some gay men had left the republic and were now beginning to tell their stories to gay rights groups.
She said there was no gay "community" as such in Chechnya. Small groups would connect by phone but ran the risk of discovery because of the monitoring of calls by Chechen security services.
Gay individuals lived, Sokirianskaia said, in a climate of fear, paranoid about being discovered.
Even human rights officials in Chechnya are unsympathetic on LGBT issues. Heda Saratova, head of the Human Rights Council in Chechnya, dismissed the article in Novaya Gazeta as "spitting into our face, our traditions, our customs."
Saratova told CNN by phone that "even if people with non-traditional sexual orientation are present in our society, no one would ever know about this. They (gay rights groups) say that they want to hold gay parades here, this is just absurd."
Ramzan Kadyrov, leader of Chechnya since 2004, has stifled any form of dissent, subduing the separatist movement that fought the Russian army for nearly two decades.
In 2009, Kadyrov said in a newspaper interview that "Prostitution, drugs and gays are the poison of our time. How can Russia support gay clubs?"
"There is a whole system aimed at weakening the country, the will, honor, and spirit," Kadyrov said of what he considered vices.
He has also spoken favorably of polygamy.
Kadyrov posts social media videos of himself working out
and offered to raise a volunteer force to send to Syria to fight on behalf of the regime of President Bashar al-Assad.
LGBT groups across Russia say they are frequently discriminated against
, and several of their rallies have been attacked and broken up
In 2013, Putin signed a law that barred public discussion of gay rights and relationships anywhere that children might hear it. The law has been condemned by Russian and international rights groups.
Human Rights Watch described the anti-gay propaganda law as "a profoundly discriminatory and dangerous bill that is bound to worsen homophobia in Russia."