Two people were killed and six injured in an explosion and fire at a military unit in Russia's northwestern Arkhangelsk region, the Defense Ministry said, while a rise in radiation levels was reported in a nearby city.
The ministry said a fire broke out after a reaction engine exploded on August 8 "when testing a liquid-propulsion system."
Regional authorities said that the explosion and fire took place near the town of Nyonoksa, where a navy ballistic-missile test range for nuclear submarines is located.
There have been "no harmful chemicals released into the atmosphere," the Defense Ministry said, adding that "radiation levels are normal."
However, the nearby city of Severodvinsk, located some 30 kilometers away, said a "brief spike" in radiation levels was registered after the blast.
“Sensors in Severodvinsk recorded a short-term increase in radiation levels. Currently, the levels have returned to normal,” according to a statement on the city’s website, citing readings between 11:50 a.m. and 12:30 p.m. local time.
Citing data from the Emergencies Ministry, Greenpeace said radiation levels had risen 20 times above the normal level in the city, Reuters news agency reported.
The environmental group asked the national consumer watchdog to establish the cause of the spike and how high radiation had risen, as well as any health risks.
Meanwhile, shipping in certain parts of Dvina Bay in the White Sea nearby was closed off for a month.
The deputy head of the Archangelsk port, Sergei Kozub, told the BBC that the closure had been planned in advance.
Nyonoksa is located on the coast of Dvina Bay in the White Sea in the Russian Arctic, about 40 kilometers west of Archangelsk, a major port used for exporting oil products and coal.
The blast is the second deadly explosion at a military site in Russia in three days.
On August 6, one person died and eight people were wounded in a series of blasts at an ammunition depot in the Siberian region of Krasnoyarsk.