The funerals of the fourteen Russian navy officers who died when a fire broke out on their submarine in the Barents Sea on July 1 were held on Saturday.
The cemetery in St Petersburg was cordoned off by the military as their relatives and senior naval officers laid them to rest.
They were interred next to the graves of some of the crew members of the Kursk, a naval submarine that sank in 2000, killing all of the 118 sailors on board. That was Russia's worst submarine disaster.
The Kremlin has said it won't release much information as it was on a secret mission, however it has confirmed that the submarine was nuclear powered and that its reactor was not damaged.
It said that toxic fumes killed the men after a fire broke out in the vessel's batteries and that some others survived, although it did not confirm how many.
Several of those killed were top-ranking naval officers, an indication that the sub may have been conducting new manoeuvres or testing.
Russian media have reported that it was a secret surveillance and research sub known as the Losharik.
After the ceremony, journalists were allowed to visit the cemetery.