In response to the Oslo bombing, Denmark's justice minister told Danish national radio on Monday that he might be interested in passing a law that requires a company that "suddenly buys an unusually large amount of fertiliser" to file a report.

Anders Breivik reportedly bought six tonnes of fertiliser from a Norwegian seller earlier this year. Artificial fertiliser is rich in ammonium nitrate - sometimes up to 34 per cent of the product is made of the chemical, which can be used as a high explosive.