Russia’s state nuclear agency Rosatom said early on Saturday that five of its staff members had been killed in an accident during tests on a military site in northern Russia. The accident occurred during tests on a liquid propellant rocket engine.

Russian authorities had previously said that two people had been killed in the incident and that a nearby city had reported a rise in radiation levels when the rocket engine blew up at a testing site in the Archangelsk region on Thursday.

Authorities said they had been forced to shut down part of a bay in the White Sea to shipping as a result.

Although the defence ministry initially said that no harmful chemicals were released into the atmosphere and that radiation levels were unchanged, authorities in the nearby city of Severodvinsk reported what they described as a brief spike in radiation. No official explanation has been given for why such an accident would cause radiation to spike.

Russia’s state nuclear agency Rosatom said early on Saturday that five of its staff members had been killed in an accident during tests on a military site in northern Russia. The accident occurred during tests on a liquid propellant rocket engine.

Russian authorities had previously said that two people had been killed in the incident and that a nearby city had reported a rise in radiation levels when the rocket engine blew up at a testing site in the Archangelsk region on Thursday.

Authorities said they had been forced to shut down part of a bay in the White Sea to shipping as a result.

Although the defence ministry initially said that no harmful chemicals were released into the atmosphere and that radiation levels were unchanged, authorities in the nearby city of Severodvinsk reported what they described as a brief spike in radiation. No official explanation has been given for why such an accident would cause radiation to spike.