The Kremlin on Wednesday refused to reveal the full story of a fire that killed 14 officers on what was reportedly a nuclear-powered mini-submarine, saying the details of the tragedy were a "state secret."
Putin's spokesman explained the secrecy surrounding the tragedy by saying the information "belongs to the category of state secrets."
Shoigu - who was on Wednesday in Severomorsk, the restricted-access military port in the Russian Arctic -- said the vessel was conducting "important research on the hydrosphere of the earth" in the Barents Sea and that those on board were "unique military specialists."
Putin has ordered a full investigation into what he called a "tragedy," saying the submersible was "not an ordinary vessel."