A protest led by neo-Nazi leader Dmitri Demushkin erupted outside the court building Tuesday. Moscow police said six protesters, including Demushkin, were detained, while several dozen others chanted "Shame!" A similar protest took place in the western Siberian city of Novosibirsk.
Hundreds of riot police gathered outside the Kremlin, where they blocked off Red Square and limited access to the adjacent Manezh Square to prevent a nationalist rally. Two years ago, thousands of ultranationalists clashed with police and beat dark-skinned passersby on Manezh Square to protest the shooting of a Russian soccer fan by a group of Caucasus men.
A top human rights advocate urged Russians not to escalate ethnic tensions following Mirzayev's release.
"There is no need to turn this everyday conflict into an inter-ethnic collision," Mikhail Fedotov was quoted by the Interfax news agency as saying.
But thousands of angry comments made the conviction one of the top Twitter hashtags in Russia.
"Such verdicts might trigger a social explosion," opposition leader and outspoken Kremlin critic Vladimir Milov tweeted.
Other comments suggested that Mirzayev's release was prompted by pressure from the Kremlin and Caucasus leaders.
"The regime is more afraid of a small riot in the Caucasus than a big one throughout Russia," opposition activist Nikolai Permyakov tweeted.
Opposition leader Alexei Navalny years ago coined a phrase urging the Kremlin to "stop feeding the Caucasus" and until this year was among the organizers of the Russian March, an annual rally of ultranationalists that also draws neo-Nazis, monarchists and militant Orthodox Christians.