A radioactive leak has been reported at a nuclear research reactor in southern Norway, authorities have said.

The reactor at the Institute for Energy Technology (IFE) in Halden leaked radioactive iodine, the Norwegian Radiation Protection Authority (NRPA) said.

Those working at the reactor at the time of the discharge on Monday were evacuated from the facility.

The leak has now been contained, the IFE said.

In a statement, the NRPA said the fault occurred "due to a technical failure during treatment of the fuel in the reactor hall".

The incident is not expected to harm the environment outside the reactor, it added.

NRPA director Per Strand said: "Our focus now is that IFE stopped the spill.

"We are in continuous contact with the IFE.

"We will open a new supervision relating to this incident to uncover how this could happen and why we were not notified until the day after."

The IFE reactor is close to the border with Sweden, but the Swedish Radiation Safety Authority says it did not detect any radiation after the discharge.

Radioactive iodine, also known as I-131, is used in small doses to treat thyroid cancer.

It has also been used to treat overactive thyroid disorders.

(Sky News)