The government has decided to extend the distribution of iodine tablets to protect residents in case of a serious accident at one of Switzerland’s five nuclear power plants.

The interior ministry said the number of people receiving a box with 12 tablets would nearly quadruple to 4.6 million, covering residents in the cities of Zurich, Basel and Lucerne.

Iodine is an established treatment against nuclear radiation. The tablets contain potassium iodide, a salt that helps prevent radioactive iodine from being absorbed by the thyroid gland.

Wednesday's move comes in response to the accident at the Fukushima nuclear plant in Japan in 2011.

In 1993 the Swiss government began handing out tablets to residents living within 20km of a nuclear reactor.

The cost for the extension, an estimated CHF30 million ($32.9 million), will be covered by the power companies after the cantonal authorities refused to fund the programme.

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