There isn't any conceivable reason why Iran needs a ...

There isn't any conceivable reason why Iran needs a missile of intercontinental range if it's worried about regional security issues. It already has, in the Shahab-3, a missile that should allow it to deter or intimidate, if that's its goal, its neighbors. So it's a little puzzling why they would want missiles of longer range, but apparently they are working on those.