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.
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.
During a ceremony in the Kremlin on Thursday, Russian President Vladimir Putin awarded posthumously orders of courage to the scientists who were killed, saying they conducted “critically important” work on “cutting-edge and unprecedented” military technologies.
“They were involved with the most complex, responsible and critically important sphere,” said Putin, according to Tass. “We are talking about cutting-edge and unprecedented technical ideas and solutions, about the weapons that will ensure Russia’s sovereignty and security for decades to come,” he added.
Putin’s “invincible” weapons
During his annual address to the Russian parliament last March, Putin boasted Russia’s military might and showed animations of what he claimed was new weaponry that could render NATO defenses “completely useless.”
Putin also claimed that Russia had developed an “invincible” missile that can deliver a warhead at hypersonic speed, as well as other weapons, including unmanned underwater vehicles capable of moving at very high speeds.
“Russia still has the greatest nuclear potential in the world, but nobody listened to us,” he said. “Listen now.”
US and international military experts have taken Putin’s words with a grain of salt. “Nobody knows how much is bluster,” Richard Aboulafia, vice president of analysis at the aerospace and defense consultancy Teal Group, told CNN at the time.
Putin has so far maintained that Russia’s development of military technologies is only for defense purposes.
“We’ve never had an intention of attacking anybody,” Putin said in his March remarks. “Russia will only retaliate if it is attacked.”
CNN’s Nathan Hodge contributed to this report.