A doctor who helped treat victims of the mysterious nuclear blast in Russia more than two weeks ago has traces of radiation in his muscle tissue, said regional officials, who blamed the readings on his diet rather than the explosion.

“Cesium-137 ... has the feature of accumulating in fish, mushrooms, lichens, algae,” Russian specialists told regional officials on Friday, according to Meduza, an independent Russian media organisation. “With a certain degree of probability, we can assume that this element got into the human body through the products of food.” They said the man was not in danger.

Meduza quoted an anonymous medical worker who said the man was asked at the hospital if he had gone on holidays in the past few years. “He said he’d been to Thailand at some point. When they heard this, they said where there’s Thailand, there’s Japan: ‘You must have eaten some Fukushima crabs!’”

More than 100 Russian medical workers have undergone checks after the incident at the Russian navy range in Nyonoksa on the White sea on 8 August, which killed five nuclear engineers, two servicemen and injured six others.

The administration’s latest statement came after Russian media reports claimed dozens of medical workers had been exposed to radiation.

Reports emerged that medical teams at the Arkhangelsk city hospital had not been warned that they would be treating people exposed to radiation and had lacked elementary protective gear. They also said Russia’s security agency had forced the medical workers to sign non-disclosure papers.

The workers, who spoke on condition of anonymity fearing official reprisals, said many doctors and nurses were angry the authorities had put their lives at risk.

A Kremlin spokesman, Dmitry Peskov, questioned whether the anonymous sources were accurate and alleged that certain forces could be interested in making false allegations about radioactive threats.

The Russian defence ministry at first denied any radiation leak even as authorities in Severodvinsk reported a spike in radiation and advised people to stay indoors and close windows. Terrified residents rushed to buy iodine, which can help reduce risks from exposure to radiation.

Russia’s state weather and environmental monitoring agency said the peak radiation reading in Severodvinsk on 8 August briefly reached 1.78 microsieverts per hour in just one neighbourhood, about 16 times the average. Peak readings in other parts of Severodvinsk varied between 0.45 and 1.33 microsieverts for a couple of hours before returning to normal.

Two days after the blast, two Russian-operated monitoring stations ceased transmitting data, when a projected radioactive plume from the deadly accident was expected to reach them, leading to accusations Russia was concealing valuable data that could help determine the technology that was being tested.

The Russian president, Vladimir Putin, has said the victims were doing “very important work for the nation’s security” but did not say what type of weapon they were testing.

Some have said the explosion occurred during tests of Russia’s prospective Burevestnik nuclear-powered cruise missile that was code-named “Skyfall” by Nato.

Associated Press contributed to this report