Gold prices firmed on Wednesday, riding on renewed safe-haven demand as fears about Greece's debt crisis returned after its government shocked the markets with a call for a referendum on a European Union aid deal. US gold rose as much as 1 percent to $1,729.4 an ounce, and eased slightly to $1,725.20 by 0640 GMT. Spot gold inched up 0.3 percent to $1,723.39.