Officials in a northern Russian city have confirmed one of the doctors who treated victims of an apparent explosion during a rocket test was found to have a radioactive isotope in his body.

Key points: Authorities have pinned the blame on a radioactive isotope being found in a doctor's body on seafood

Authorities have pinned the blame on a radioactive isotope being found in a doctor's body on seafood Russia's nuclear agency said the explosion occured during a rocket test on a sea platform

Russia's nuclear agency said the explosion occured during a rocket test on a sea platform After a spike in radiation levels was reported two days after the incident, the agency conceded it involved nuclear materials

The local health ministry blamed the trace amounts of radioactive material on bad seafood after the doctor treated patients from an area where a radiation spike was recorded.

"Cesium-137 … has the feature of accumulating in fish, mushrooms, lichens, algae," the statement posted on the local government's website read.

"With a certain degree of probability, we can assume that this element got into the human body through the products of food."

Secrecy surrounding the explosion sparked fears of a cover-up in Russia, with authorities backflipping on orders to evacuate a nearby village.

State nuclear agency Rosatom said the accident occurred during a rocket test on a sea platform.

The rocket's fuel caught fire after the test, causing it to detonate, it said in a statement carried by Russian news agencies.

Two days later, after a spike in radiation levels was reported, Rosatom conceded the accident involved nuclear materials.

The Russian military ordered residents of the small village of Nyonoksa to temporarily evacuate, citing unspecified activities at the nearby navy testing range.

But a few hours later, it said the planned activities were cancelled and told the villagers they could go back to their homes, said Ksenia Yudina, a spokeswoman for the Severodvinsk regional administration.

Local media in Severodvinsk said Nyonoksa residents regularly received similar temporary evacuation orders, usually timed to tests at the range.

Russia's state weather service said radiation levels spiked in the Russian city of Severodvinsk, about 30 kilometres west of Nyonoksa, by up to 16 times following the explosion.

Emergency officials issued a warning to all workers to stay indoors and close the windows, while spooked residents rushed to buy iodide, which can help limit the damage from exposure to radiation.

ABC/wires