"On Thursday, 27 July, Sweden reported that an incident occurred at its Forsmark 1 reactor... They rated the incident at Level 2 according to the 7-level International Nuclear Event Scale (INES)," IAEA spokesman Ayhan Evrensel said.

"Swedish authorities have not requested any assistance from the IAEA," he added.

According to the scale, level 2 qualifies as an "incident," just one step above an "anomaly".

It is less critical than a "serious incident," and far below the level 7 "major accident" that was the explosion at Chernobyl in 1986, which projected a large quantity of radioactive material beyond the plant's perimetre.

"Incidents" involve a "significant failure in safety provisions but with sufficient defence in depth remaining to cope with additional failures," in other words, a "significant spread of contamination" or "overexposure of a worker" to radioactive material, according to the IAEA.

The Swedish Nuclear Power Inspectorate (SKI) said Thursday it would open an investigation into the incident.

Swedish authorities have shut down five of the country's reactors, four of them in connection with a potentially dangerous failure caused by an electricity blackout at the Forsmark 1 plant last week.

Following the shutdown, the environmental organisation Greenpeace called Friday for worldwide testing of nuclear power plants.

Nuclear power accounts for nearly half of Sweden's electricity production.

A source close to the UN atomic watchdog told AFP the IAEA "was not alarmed" and televised reports speaking of a near catastrophe were exaggerated.

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