Russian's state nuclear company says five people were killed in Thursday's rocket explosion on a naval test range.
A statement from Rosatom said three people were also injured in the incident.
They say the staff members suffered serious burns in the accident, which has been shrouded by mystery.
On Friday Russian government sources said two people died and six were injured in the Nyonoksa blast.

Thai teen kills 7 in rampage at home and school before shooting himself
US appeals court blocks Trump’s $400 million White House ballroom project
Spain dismantles one of Mediterranean's largest human smuggling networks
Syria says bomb on minibus near Damascus wounded 14, deaths reported mistakenly
Spain hopes to transfer migrant minors to mainland within weeks
