On the same day Russia belatedly admitted that the mystery explosion which released radiation into the air last Thursday - and had triggered warning alerts across towns in northern Russia - involved a “small-scale nuclear reactor”, President Trump tweeted concern over the radiation leakage.

Radiation levels had spiked to 20 times their normal levels after the incident at a military testing ground in Russia’s Arkhangelsk region, prompting an emergency response team to deploy in full nuclear radiation protective gear, as photos which came out in the aftermath appeared to show.

The United States is learning much from the failed missile explosion in Russia. We have similar, though more advanced, technology. The Russian “Skyfall” explosion has people worried about the air around the facility, and far beyond. Not good! — Donald J. Trump (@realDonaldTrump) August 12, 2019

"The United States is learning much from the failed missile explosion in Russia," Trump stated late in the day Monday. He added concern over the "air around the facility" which area residents have been exposed to and could possibly impact neighboring areas.

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

Local Russian media photo showing emergency response united in full chemical/radiation protective suits.

Consistent with early speculation, western defense officials and analysts now believe it was a failed test of a Russian nuclear powered cruise missile.

One US defense analysts has pointed to "an experimental nuclear-powered cruise missile known in Russia as the 9M730 Burevestnik and by Nato as the SSC-X-9 Skyfall" — precisely the type of nuclear-powered weapon Putin had previously touted among Russia's developing hypersonic arsenal in a 2018 speech. This is the "Skyfall" reference Trump made in his tweet.

Though within two days following last Thursday's accident - believed to have happened on a sea platform, which resulted in an area of a White Sea port being shut down - Russia's nuclear agency Rosatom, admitted it had been testing an “isotope power source in a liquid propulsion system,” there's now greater confirmation it involved a cutting edge hypersonic cruise missile.