"Five people died during tests of a liquid-propellant engine system as a result of the accident at a military range in the Arkhangelsk Region. Three other colleagues received wounds and various burns," the company said.
It added that the accident took place during engineering and technical works on isotope sources of the engine.
All those wounded had been hospitalized, Rosatom pointed out, expressing condolences to the families of the accident victims.
The accident happened on Thursday, when a blast, followed by a fire, happened during the tests. The Defence Ministry has said back then that two people were killed in the accident.
Later, a source reported that specialists from Rosatom as well as the Defence Ministry were killed as an experimental engine system ignited at a site.
The incident happened in a military unit in the village of Nenoksa, according to the press service of the Arkhangelsk region governor.
The central marine test site of the Russian Navy is situated on the territory of the Nenoksa administrative district.