The head of the Russian Federal Atomic Energy Agency (Rosatom) revealed Monday the circumstances of the death of five nuclear experts in a mysterious explosion at sea.
The Russian official confirmed that the five experts who died last week in the nuclear explosion were working to develop "new weapons", vowing to continue tests "to the end" despite the incident.
The incident occurred last Thursday at a military facility in the Arctic region on the coast of the White Sea, but Russian authorities waited until Saturday to admit that it is nuclear. The explosion caused a brief rise in radioactivity.
Russia awarded medals to experts as "national heroes" who died, while the city of Sarov - home to Russia's main nuclear research base - declared mourning.
The TASS news agency quoted officials as saying that the fuel caught fire in the rocket, causing the explosion. The force of the blast threw several people into the sea.
Nuclear experts in the United States said they suspected the blast occurred during a test of a cruise missile capable of carrying nuclear warheads that Russian President Vladimir Putin boasted last year.
Valentin Kostyukov, head of a nuclear center affiliated with Russia's state-owned nuclear company Rosatom, described the experts as "the elite of the Russian Federal Nuclear Center and conducted the test under incredibly difficult conditions."
Although the Defense Ministry initially said there had been no change in the radiation level, authorities in the nearby city of Severodvinsk reported what it described as a brief increase in the radiation level, without giving an explanation.
During the Cold War, Sarov was a secret research center, known as Arzamas-16, where the first Soviet nuclear weapons were made. Today, the city remains closed, and only those with private licenses are allowed in.