An explosion that killed five Russian scientists during a rocket engine test this month was followed by a second blast two hours later, the likely source of a spike in radiation, Norway's nuclear test-ban monitor said on Friday. The second explosion was likely from an airborne rocket powered by radioactive fuel, the Norsar agency said — though the governor of Russia's Arkhangelsk region, where the blast took place, dismissed reports of another blast.

"The aftermath of the incident does not carry any threat," the governor, Igor Orlov, told Interfax. "Everything else is yet another round of disinformation." Russia's Defense Ministry did not immediately respond to a request for comment when contacted on Friday. There has been contradictory information about the Aug. 8 accident near the White Sea in far northern Russia and its consequences. The Defense Ministry initially said background radiation remained normal, while the state weather agency said radiation levels had risen. Russia's state nuclear agency, Rosatom, said on Aug. 10 the accident involved "isotope power sources" but did not give further details.