Civilians of two northern Russian cities flocked to pharmacies Friday to purchase large quantities of iodine after a mysterious explosion at a nearby military testing site Thursday.

Russia’s Ministry of Defense stated that two people were killed and six injured after a liquid-propelled rocket engine exploded at the site, adding that the incident did not release any harmful chemicals into the atmosphere.

They also reassured that radiation levels in the region remained stable, but refused to give further details, Reuters reports.

However, authorities in the nearby port city of Severodvinsk reported a spike in radiation levels in the area, and are unsure why the accident would cause such changes. Data cited by Greenpeace from Russia’s Ministry of Emergency Situations showed radiation levels rose 20 times above the normal level in the city, about 18 miles from the testing site.

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“Everyone has been calling asking about iodine all day,” a pharmacy said.

The large demand for iodine also spread to pharmacies in Russia’s northern port city of Arkhangelsk, which strained their iodine supplies until the point of exhaustion.

“We still have iodine left,” an Arkhangelsk pharmacy stated, “but a really large number of people have come in for it today.”

Authorities have since shut down an area of the Dvina Bay in the White Sea, near the testing site, without elaborating on specifics of the closure; an unidentified naval officer only stated that the explosion could have caused a toxic fuel spill.

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Nyonoksa, a village near the site of the accident, is reportedly another location where weapons, such as ballistic and cruise missiles, are tested and used by the Russian navy.

The incident came days after massive explosions at a military ammunition depot in Siberia, resulting in eight injuries. That same facility, near the city of Achinsk, had another explosion Friday, when it was reportedly hit by lightning.

Fox News' Morgan Cheung contributed to this report.