Fourteen Russian sailors have been killed in a fire on one of the navy’s underwater research vessels, the worst naval disaster for the country since 2008. The Russian Defense Ministry said Tuesday that the fire released fatal “toxic fumes” inside the secretive, “nuclear-powered” submersible meant to go deep underwater. The ministry also denied reports of a gas explosion on the vessel after Norwegian authorities said they had been told by Russian officials that a gas explosion was to blame. It’s unclear how many sailors were on board at the time. “It’s a huge loss for the navy. I offer my sincere condolences to the families of the victims,” Russian President Vladimir Putin said, adding that two of those on the vessel’s “highly professional” crew had been awarded the nation’s highest honorary title, the Hero of Russia. Seven of those killed also held the rank of captain, he said. In 2008, 20 sailors were killed on another nuclear-powered submarine after a firefighting system was accidentally switched on during sea trials.