A senior White House official echoed President Donald Trump's previous tweets to say that Washington believes a Russian hypersonic cruise-missile program is linked to the deadly August 8 explosion that killed at least five people, Reuters reported.
Speaking on condition of anonymity, the official said Washington wasn't ready to assert that it was a nuclear explosion but believed radioactive elements were involved.
An evacuation of Nyonoksa, the town where the blast occurred near the Arkhangelsk naval test site, was scheduled for August 14, but was later canceled.
However, the Rosgidromet weather agency on August 13 added further evidence to reports that the test at the Nyonoksa range on the White Sea had released not only toxic missile fuel but also unspecified radioactive material.
And The New York Times on August 12 cited anonymous U.S. intelligence officials who said Russia was apparently testing a "new type of nuclear-propelled cruise missile," while saying the blast could possibly be "one of the worst nuclear accidents in the region since Chernobyl."
In a post to Twitter on August 12, U.S. President Donald Trump also asserted that the incident was a failed test of a missile prototype nicknamed Skyfall by NATO experts, though he gave no evidence.
Last week's incident continues to be dogged by confusion and misinformation from local and federal officials, both about the exact death toll but also about what exactly was being tested.
In a briefing on August 13, Kremlin spokesman Dmitry Peskov gave little new information about the explosion.
"Accidents, unfortunately, happen. These are tragedies. And in this case it is important for us to remember those heroes who lost their lives as a result of these accidents," Peskov was quoted by Russian news agencies as saying.
Residents of the city of Severodvinsk, around 30 kilometers east of Nyonoksa, reportedly bought out iodine drops from city pharmacies in the hours after the first reports emerged; iodine is often taken to protect the thyroid gland from some types of radiation.
In its statement published by the state news agency TASS, Rosgidromet cited data collected by a northern regional monitoring agency, saying that gamma radiation jumped by 4 to 16 times normal levels in Severodvinsk on August 8.
TASS also cited an official with the state-run nuclear agency Rosatom as saying the levels were harmless for humans.
An earlier report published on August 8 by Arkhangelsk regional emergency officials said radiation had risen to 20 times normal levels. That report was circulated by the environmental group Greenpeace.
The Severodvinsk city administration had also published a statement on August 8 reporting an increase in radiation, though that statement was later taken down from its website.
No definitive death toll has been released.
In a video published on a Sarov city news website on August 11, Vyacheslav Solovyov, a nuclear researcher at the main nuclear research facility in Sarov, said the researchers had been investigating, among other things, "the creation of small-scale sources of energy using radioactive fissile materials."
In its latest statement on the incident, Norway’s radiation monitoring agency on August 12 said that it hadn't recorded any uptick in radiation levels by its monitoring equipment.