MANSUR MIROVALEVMOSCOW (AP) â¿¿ A world martial arts champion from Russia's southern Caucasus region was convicted Tuesday of involuntary manslaughter, but set free after a trial that inflamed ethnic tensions. The verdict led to protests by nationalists outside the court and prompted Russian riot police to flood the wide square outside the Kremlin to prevent possible violent clashes between nationalists and ethnic minorities from the Caucasus. Rasul Mirzayev had punched former police academy student Ivan Agafonov outside a Moscow nightclub in 2011 after the drunken 19-year-old offended Mirzayev's girlfriend. Agafonov fell down, hitting his head on a sewer grate, and died four days later. Mirzayev's trial had raised the anger of nationalists, who accused him of deliberately killing the Russian student. The athlete's supporters argued that Agafonov had provoked the lethal punch and his killing was accidental. The Zamoskvoretsky court ruled Tuesday that since Mirzayev had already served his sentence while in custody awaiting trial he could walk free. There are significant tensions between ethnic Russians, who make up two-thirds of the country's 142 million people, and dark-complexioned Muslims from the Caucasus, where there are more than 100 ethnic groups. Hundreds of thousands of Caucasus natives have flooded central Russia in search of jobs, causing a clash of cultures that aggravates deeply ingrained xenophobia. Mirzayev, a bearded and lean 26-year-old, comes from Dagestan, Russia's most multiethnic province. Dagestan has for years been an epicenter of an Islamic insurgency that stems from separatist wars in neighboring Chechnya. The Caucasus has also been beset by high unemployment and rampant corruption. The Kremlin has spent billions of dollars to subsidize the restive region, but government critics say most of the money is embezzled by local leaders. Polls show that nearly half of Russians resent the Kremlin subsidies and dislike migrants from both the Caucasus and the former Soviet states in Central Asia.