The U.S. official also said that increased levels of radiation had been detected in areas near the site of last week’s explosion.
It remains unclear if the radiation levels and the explosion were linked to a possible launch of the new missile system.
On Monday afternoon, President Trump tweeted about the incident.
Called the 9M730 Burevestnik by Russia and the SSC-X-9 Skyfall by NATO, the cruise missile features a small nuclear-powered engine that enables it to fly long distances and conceivably allows it to circumvent missile defense systems.
First unveiled by Russian President Vladimir Putin on March 1, 2018 as being “invulnerable” to missile defense systems, Russia has continued promoting the program. Last July the Russian Defense Ministry released video of what it said was a successful missile launch as well as images of the missile under development.
But U.S. officials have said that the missile is not operational and has experienced multiple crashes, including a crash in the Russian Arctic.
Last Thursday, the Russian Defense Ministry acknowledged there had been explosion at the Nenoksa Missile Test Site along the coast of the Arkhangelsk region in northwestern Russia that killed two service members and injured six others. The Ministry said the explosion was triggered by a test of a liquid fueled propulsion engine.
TASS, Russia’s state news agency, reported that the explosion occurred on a floating launch platform off the coast.
But Russian authorities cloaked the incident in secrecy and have released few and conflicting accounts in state media.
Nenoska’s local government initially posted a report of a spike in radiation at the site on its website, but that report removed after the defense ministry said no elevated radiation levels had been detected.
Late Sunday, the Russian Federal Nuclear Center, which operates under Russia’s state atomic agency, Rosatom, confirmed that the test involved the testing of nuclear power sources and that five of the center’s specialists had also died in the explosion and three more were injured.
Alexander Chernishev, the Center’s deputy director, said in a video interview that its experts had recorded a spike but that it only lasted an hour.
“No lingering nuclear pollution has been recorded either by our experts or external ones,” Chernishev said.
Russia’s lack of information about the incident and its secretive official response has prompted comparisons with the Chernobyl disaster in 1986. Local residents in the area were reported by Russian media to be buying up iodine pills, used to prevent radiation poisoning.
Russia has never given details on how the the new missile works but most arms experts believe it is a so-called ramjet—that is an engine that works by sucking in air, heating it and then releasing it out the back to create propulsion. The miniature nuclear-reactor heats the air.
The United States abandoned the development of a similar program in the 1960’s, leading outside experts to question whether the concept of a nuclear powered missile is feasible.
Cheryl Rofer a veteran scientist who formerly worked at Los Alamos Laboratory and who said she had been personally acquainted with the U.S. ramjet program, in a< href="https://nucleardiner.wordpress.com/2019/08/11/speculations-on-the-nenoksa-explosion/"> blog post Sunday wrote that the Kremlin had likely been persuaded to back an unrealistic program.
“I think that what has happened is that someone sold a program to Putin. The visuals are cool, and the idea of a cruise missile that can just keep cruising obviously appealed to him. The promoter of the program may even believe in it,” Rofer said. “ I’m saying I think they’ll never have an operating system.”
Russia's development of the new cruise missile was not restricted by existing nuclear arms reduction agreements with the United States including the recently scrapped Intermediate Nuclear Forces (INF) Treaty.