These include developing a plan to maintain and upgrade emergency bunkers across the country, many of which have been sold or allowed to fall into disrepair.

“Operations centres in bunkers need to continue to be held in ready reserve. In special cases, decommissioning or sale can take place, but first there must be a dialogue between MSB and the local region,” the letter warned.

Sweden’s government decided to bring back civil defence last year as part of its defence policy for 2016 to 2020.

"There is nothing to suggest that war is likely, but we have been given an order from the government to plan for it,” Svante Werger, the press officer for MSB, told the Sydsvenskan newspaper.

The letter has provoked complaints from some municipalities that they have insufficient information on what is required and have not been provided with the necessary funding.