All 84 passengers and eight crew members on the Russian military's Tu-154 plane are believed to have died when it crashed two minutes after taking off from Russia's Sochi.
Transport Minister Maxim Sokolov said in televised remarks on Monday that investigators are looking into a possible pilot error or a technical fault and that a terrorist attack was not among the main theories, the Associated Press reported.
Rescue teams on Monday continued to search for victims after the plane on its way to Syria crashed into the Black Sea shortly after takeoff. The passengers included dozens of singers in Russia's world-famous military choir.