The sample was collected at an air filter station in Svanhovd, in North Norway near the border with Russia, from August 9-12.

On August 10, Russia's nuclear agency Rosatom said five people were killed in an explosion at the Arkhangelsk site in the far north. It later said they were testing new weapons.

"At present it is not possible to determine if the last iodine detection is linked to the accident in Arkhangelsk last week," the Norwegian Radiation and Nuclear Safety Authority said in a statement.

It said Norwegian stations detect radioactive iodine about six to eight times a year, and "the source is usually unknown".

Immediately after the accident, Russia's defence ministry said there had been no radioactive contamination.

Local authorities in Severodvinsk, near the site, last week initially published information about a spike in radiation, but later deleted it and a local official said that radiation levels were not above the norm.

However, radiation levels were up to 16 times the norm in Severodvinsk immediately after the accident, Russia's national weather service Rosgidromet said on Tuesday. The levels returned to normal after 2.5 hours.