More than 800 people have been arrested in central Moscow in an attempt to prevent further ethnic clashes over the shooting of a football fan, police say.
The arrests came as groups of youths, many shouting nationalist slogans, gathered near a Moscow train station.
The death of a Moscow Spartak fan, allegedly in a fight with North Caucasians, has prompted riots and attacks targeting ethnic minorities.
Dozens more people were reportedly detained in other Russian cities.
Police in St Petersburg held 60 people and another 100 were arrested in Samara, according to Interfax news agency.
Moscow city police spokesman Vitkor Biryukov told Interfax that most of the arrests were at the city's Kievsky railway station.
"We have confiscated several air guns, knives, clubs and and stun guns," he said, adding that there had been no serious incidents in the city and that the most aggressive elements among the youths had been removed from the scene.
Moscow Mayor Sergey Sobyanin called for calm.
"I would call on hotheads not to submit to provocation and appeals to violence," he said.
"The police will continue to firmly suppress any attempts at provocation and violence."
Reports said about 300 youths gathered around a shopping mall near the station, forcing it to close, and others tried to block a nearby road.
Many were shouting slogans such as "Russia forward" or "Russia for the Russians".
Police patrols have been stepped up throughout central Moscow, and huge traffic jams have been reported.
A police source told Interfax the heavy police presence would continue deep into the night.
Special police units from outside Moscow and Interior Ministry troops have also been brought in.
On Saturday, thousands of people clashed with police outside the Kremlin over the shooting of Mr Sviridov.
Police have promised to complete an investigation into Mr Sviridov's death, which happened last week.
Aslan Cherkessov, 26, from the Kabardino-Balkaria region in the Caucasus, has been formally accused of the murder by a Moscow district court and placed in custody until 6 February.
While ethnic minorities complain of continuing discrimination in Russia, some ethnic Russians accuse the authorities of trying to play down hate crimes against Russians.
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