Russian President Vladimir Putin on Thursday said that the five scientists killed in a nuclear explosion in the northwestern part of the country last August were working on the “most advanced and unparalleled” weapons in the world.

Putin was speaking to relatives of the fallen men during a televised state awards ceremony at the Kremlin, assuring them that the scientists had been doing “critically important” work, The independent Moscow Times reported.

Putin didn’t specify the weapons, but U.S. defense officials believe it was what Russians call the 9M730 Burevestnik missile, which NATO has designated the SSC-X-9 Skyfall.

RUSSIA NUCLEAR MISSILE EXPLOSION RESULTED IN RADIOACTIVE ISOTOPES FOUND IN TEST SAMPLES AFTER ACCIDENT

The missile was first revealed by Putin in March 2018 along with other doomsday weapons.

“We’re talking about the most advanced and unparalleled technical ideas and solutions, about weapons designed to ensure Russia’s sovereignty and security for decades to come,” Putin said. "No matter what, we’ll certainly keep improving this weaponry.”

Putin claimed that possessing the weapons “is the most important reliable guarantee of peace on the planet today," The Times reported.

CLICK HERE TO GET THE FOX NEWS APP

The August explosion was followed by a brief rise in radiation levels in nearby Severodvinsk, Russia, a city of 183,000. Authorities insisted the recorded levels didn't pose any danger to local residents. Russia's state weather agency, Rosgidromet, said earlier this month it believed radiation levels had risen up to 16 times after the accident.

Fox News' Travis Fedschun contributed to this report.