MOSCOW (AP) — Russia's defense minister has arrived at an Arctic navy base to oversee the investigation into a deadly fire on one of the Russian navy's deep-sea research submersibles.

During Wednesday's trip to Severomorsk, Sergei Shoigu will meet with members of a panel investigating the blaze which killed 14 crewmembers, according to the Defense Ministry.

The ministry said toxic fumes from Monday's blaze killed the seamen, but did not specify how many sailors were aboard the vessel at the time or whether there were any survivors. It said the ship was measuring sea depths in Russia's territorial waters.

The ministry didn't name the ship, but Russian media reported it was the country's most secret submersible, a nuclear-powered vessel nicknamed the Losharik that has been designed for sensitive missions at great depths.