A report by Russian opposition politician Ilya Yashin has warned that Chechen leader Ramzan Kadyrov has become a national security threat and should be removed.
He heads a “corrupt and dangerous” regime within Russia that operates according to its own rules, he added.
The Chechen strongman has rejected the report as “idle chatter”.
Hours before its official presentation, Mr Kadyrov leaked a copy of the document on his social media accounts.
A former separatist militant, Ramzan Kadyrov was appointed to run the southern Russian republic of Chechnya by Vladimir Putin in the wake of two brutal wars there, and now portrays himself as the president’s most devoted foot-soldier.
He sparked controversy recently by using social media to brand critics of the Kremlin as traitors.
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Mr Yashin’s 64-page report, which is collated from open sources, describes a region in which federal funds are diverted, federal laws flouted and critics harassed or even killed.
It also claims that the Chechen leader has accumulated what amounts to a personal guard of up to 30,000 men, officially interior ministry troops but deeply loyal to Mr Kadyrov personally.
The report calls for Mr Kadyrov to be questioned over alleged links to a number of high-profile murders including the shooting of opposition politician Boris Nemtsov a year ago this week. Mr Yashin is a leading member of the People’s Freedom Party (Parnas), which was set up by Mr Nemtsov.
A group of men due to stand trial for Mr Nemtsov’s murder have ties to men close to Ramzan Kadyrov, although the official investigation has made no such link.
There was tight security for the launch of the report in Moscow, but two protesters were able to enter the hall. One threw fake dollars at the podium, alluding to claims that opposition activists are paid by the West to work against Russia.
The building was then evacuated by police claiming a bomb threat. It was the second anonymous call in two days.