Small amounts of radioactive substances have been detected in air samples in Finland though there was no risk to public health, the country's nuclear safety watchdog said on Friday.

"The concentrations were very low and posed no risk to people or the environment," the Radiation and Nuclear Safety Authority (STUK) said in a statement.

STUK said that the radioactive substances did not originate from Finnish nuclear power plants, though it did not offer an explanation for their detection.

"In many cases, the source of the radioactive substances cannot be identified," the agency said. Finland, Sweden, Russia and the wider region have a number of nuclear power reactors.

-Stine Jacobsen/Reuters