Dmitry Yarosh, leader of the right-wing Pravy Sektor, reportedly posted on VKontakte during the weekend that Chechen warlord Doku Umarov should help fight against the Russian occupation of Ukraine's pro-Moscow Crimean region, RIA Novosti reported.
"Russia is not as strong as it seems. You now have a unique chance to win," the post said.
Yarosh also wrote Ukrainians and natives of Russia's North Caucasus shared "spilled blood."
Pravy Sektor, whose VKontakte page has been blocked since Sunday, denied the authenticity of the appeal to Umarov. The social network's spokesman said an unknown hacker posted the call to arms.