U.S. authorities are scrambling to clarify exactly what led to what is now confirmed as the explosion of a small nuclear reactor in the White Sea on Aug. 8 at a Russian research institute. Russian atomic agency Rosatom initially said the explosion was a rocket-engine mishap and denied that radiation levels spiked in the atmosphere shortly after the explosion. The New York Times reports that U.S. intelligence officials suspect the blast involved the so-called SSC-X-9 Skyfall nuclear cruise missile that Russian Presdient Vladimir Putin has warned could reach any corner of the earth. Late Sunday, officials at the testing site, where five of the dead scientists were stationed, confirmed to the Times that a small nuclear reactor was involved in what is likely the Kremlin’s worst nuclear accident since Chernobyl.