Electronic cigarettes are to carry health warnings in the United States under new regulations announced by the Food and Drug Administration.
The restrictions will also ban the sale of e-cigarettes to children and require packaging to list their ingredients.
E-cigarettes are battery-operated products that deliver a nicotine flavour to users in the form of an aerosol, which normally contains nicotine.
According to the latest industry estimates, there are five million users in the US in a rapidly expanding industry that generated more than €1bn in sales last year. Sales are expected to double over the next 12 months.