The FSB said in a statement today that the man resisted and was killed by security forces in the Volga River city of Nizhny Nogvorod.
An explosive device, firearms and ammunition were found at the home of the unidentified man who, according to the FSB, hailed from one of the former Soviet republics.
Russian launched a military operation in 2015 to help the Syrian government fight the IS.
Thousands of Russians and Central Asians were believed to be fighting in Syria and Iraq at the height of the Syrian civil war.
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