The new report commissioned under the Organization for Security and Co-operation in Europe (OSCE) noted "repression has gradually intensified since 2012... and reached its peak with the new reform laws adopted after the beginning of the war" in Ukraine.
According to the report, "a climate of fear and intimidation" had been created through the use of criminal law, violence against civil society activists and media, propaganda and other tactics.
The new legal provisions had led to activists, journalists, lawyers and others "to reduce or abandon their activities or to leave the country".
"Successively, all federal and regional law enforcement agencies have been brought under the direct control of the president" Vladimir Putin, it added.
Russia did not participate in the study nor respond to the expert's request to visit the country, noted the report seen by AFP and which was to be published later Thursday.
- 'Mass repression' -
It is the third report initiated by OSCE members since Russia's invasion of Ukraine in February.
The two other reports focused on Ukraine, accusing Russia of "clear patterns of international humanitarian law violations" in Ukraine.
Invited this week to address the Vienna-based OSCE, Evgenia Kara-Murza, the wife of a detained Russian activist, called on western countries to support Russian civil society.
Her husband, prominent Putin critic Vladimir Kara-Murza, was detained in late April for denouncing the Ukraine conflict and faces a prison sentence.
"It is very important to remember that this full-scale invasion of Ukraine is going on against the backdrop of mass repression in Russia," Evgenia Kara-Murza told reporters at a press conference in Vienna on Tuesday.
Evgenia Kara-Murza, who has been living in the US with the couple's three children, accused Putin of "carrying out a genocide in Ukraine" and cracking down on protest at home.
Moscow has stepped up efforts to stamp out dissent -- accusing critics of threatening national security -- since Putin sent troops into Ukraine.
Amid an unprecedented crackdown on dissenting voices in Russia, most opposition activists have been either jailed or left the country.
The OSCE was founded in 1975 -- at the height of the Cold War -- to foster relations between the Western and Eastern blocs.
Its current members include NATO countries and allies of Moscow.