Sova director Aleksandr Vekhorovsky said the deaths occurred earlier in the week when a fight broke out at a Chechen restaurant in Kondopoga, located in Russia's Karelia region.
Kondopoga police have confirmed that two people were killed and several wounded in a fight on August 30.
After the incident, Vekhorovsky said anti-immigrant groups called on Russian nationalists to come to the city.
Vekhorovsky said dozens -- possibly hundreds -- of nationalists came to Kondopoga. On September 1, he says groups of them attacked the Chechen restaurant with metal bars and gasoline bombs and fought with police.