(CNN) An accident at a Russian military test site that claimed the lives of five nuclear agency workers and sent radiation levels spiking is likely to remain shrouded in mystery, after Kremlin spokesperson Dmitry Peskov on Friday said information around the incident would stay "strictly classified."

The explosion, which happened during the summer near the village of Nyonoksa, about 30 miles west of the port city of Severodvinsk, prompted widespread international speculation that the accident involved a nuclear-powered cruise missile, known as the Burevestnik or Skyfall.

Although Russia is developing such a missile, Peskov has repeatedly declined to say what weapons were specifically tested.

"Tests of new weapon systems were involved. For this reason it is only natural that the investigation being carried out in this connection cannot be public," Peskov said, according to Russian state-run news agency Tass.

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Rosgidromet, the Russian meteorological agency, reported a brief spike in radiation levels following the incident, but Russian officials called off the evacuation of the village.

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