The main risk inside the storage facility is the chemical toxicity of uranium hexafluoride gas and fluoride compounds generated in contact with water. The radiological risk from enriched uranium at Natanz is likely to be much smaller than the chemical toxicity from the fluorine.

Destroying Iran's stores of enriched uranium would bring danger for people nearby but not trigger another Chernobyl.

Fears of catastrophe rippled through the Gulf on Thursday when the Israeli military said it had struck a site in Bushehr on the Gulf coast - home to Iran's only nuclear power station - only to later say the announcement was a mistake.