President Trump on Monday said his administration is “learning much” from a mysterious explosion in northern Russia last week that reportedly took place during the test of a nuclear missile.

“The United States is learning much from the failed missile explosion in Russia,” Trump tweeted from his golf club in Bedminster, N.J., where he is currently staying.

“We have similar, though more advanced, technology,” he added. “The Russian ‘Skyfall’ explosion has people worried about the air around the facility, and far beyond. Not good!”

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U.S. officials have not publicly spoken about the blast, which occurred last week near the Nenoksa Missile Test Site. Seven people died in the incident, which triggered a spike in radiation, prompting speculation it involved a nuclear reactor.

The New York Times reported that U.S. intelligence officials believe the blast may have involved a prototype of the SSC-X-9 Skyfall, a cruise missile powered by a small nuclear reactor that allows it to travel long distances.

Officials at a research institute where five of the scientists who died worked confirmed late Sunday that a small nuclear reactor had exploded during the test.

The explosion took place roughly a week after the U.S. formally withdrew from the Intermediate-range Nuclear Forces Treaty, a decades-old arms pact with Russia credited with helping end the Cold War.

The U.S. has blamed Russia for failing to uphold its end of the treaty, but Trump has suggested that he would be interested in brokering a new deal with Moscow and Beijing to halt nuclear proliferation.