Speculation was fueled further when the fact that many among the deceased were high ranking naval officers was revealed— unusual for a mere underwater "research" vessel.
Russian President Putin has now confirmed it was indeed a nuclear-powered submarine after officials declined to reveal even the most basic details, citing its "secret mission". As CBS reports:
Putin met Thursday with Defense Minister Sergei Shoigu, who had returned from the Navy's Arctic base of Severomorsk, and asked him about the submersible's nuclear reactor. Shoigu said the reactor is "completely isolated now" and it is "in full working order."