Five workers were killed in an accident during a missile test at a military site in northern Russia, the country’s state nuclear agency Rosatom has confirmed.
The agency refused to say whether there had been a release of radiation as a result of the accident on Thursday.
A further three staff members suffered injuries, including burns, and are receiving medical treatment in specialised facilities, the agency said.
Russian authorities had previously said two people were killed in the incident and that a nearby city had reported a rise in radiation levels when a liquid propellant rocket engine blew up at a testing site in the Arkhangelsk region.
The accident happened during the engineering and technical support of “isotope power sources” on a liquid propulsion system, Rosatom said in a statement.
Local residents have been stocking up on iodine, used to reduce the effects of radiation exposure, after the accident, local media reported.
Russia’s defence ministry has given few details of the incident after initially saying no harmful chemicals were released into the atmosphere and radiation levels were unchanged.
However, authorities in the city of Severodvinsk reported a brief spike in radiation levels after the accident.
US nuclear experts said they suspected the blast and radiation release happened during the testing of a nuclear-powered cruise missile.
Russian media reported that the rocket engine explosion may have happened at a weapons testing area near the village of Nyonoksa where regular tests on cruise and ballistic missiles are carried out.
Greenpeace said data from the Emergencies Ministry showed radiation levels had risen 20 times above the normal level in Severodvinsk, around 18 miles from Nyonoksa.