Very low levels of radiation, which are higher than normal but don't seem to pose a health hazard, are being registered in the Czech Republic and elsewhere in Europe, the International Atomic Energy Agency said Friday.

The agency said the cause was not known but was not the result of Japan's Fukushima Daiichi nuclear disaster, which spread radiation across the globe in March.

The "very low levels of iodine-131 have been measured in the atmosphere," the agency said in a statement. It said such radioisotope will lose much of its radiation in about eight days.

However, an official familiar with the matter, who asked for anonymity because he was not authorized to comment, said the release appeared to be continuing.

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