The only way to lose belly fat is to lose fat full stop! It might well be that your belly fat is the last bit of fat to go, in which case you need to diet harder, cut out more carbs or do whatever form of diet you prefer to do to lose your fat. Either that or up your exercise.

Getting your body into a fat burning rather than carb burning mode or even worse undertaking an extreme low calorie diet will do the best job of burning body fat and retaining muscle!

If you are talking about lack of muscle tone rather than excessive fat then by all means perform the exercises described above.