14 submarine sailors serving in the Russian Navy have died after a fire broke out on their research vessel, Russia’s Defense Ministry reported. The sailors died due to toxic fumes emitted by burning materials on the vessel. The victims of the fire have not yet been named.

The fire broke out in Russian waters on July 1 on a deep-sea vessel researching the sea floor of the Pacific Ocean in the interests of the Russian Navy. The Defense Ministry noted that the fire has now been extinguished and the vessel transported to a navy base in Severomorsk.

An investigation into the causes of the fire is being led by Naval Commander-in-Chief Nikolai Yevmenov.

Update: RBC reported that the vessel in question is the AS-12 atomic deep-sea station Losharik, which was constructed in the late 1980s. Other sources reported that the fire took place on a submarine.