Fortis, the Dutch-Belgian financial services group, is planning to float its US insurance unit next year in an initial public offering which could raise as much as $4.5bn (€3.9bn), in the largest IPO in the US insurance sector for a year and a half.

Anton van Rossum, chief executive of Fortis, said: "We cannot do everything everywhere. We have decided to divest a non-core element of our business and to use the proceeds to accelerate the development of our core businesses."