Are cigarettes a mental or physical addiction?

BOTH!! I agree that cigarette smoking is most like both mental and physical in its addiction but sometimes can be more mental. For instance in someone that smokes 5 or less cigarettes a day, the addiction is more psychological. Nevertheless, it is all or none when you smoke. No such thing as a "casual" smoker. Try to quit or do not ever start.
Mental and physical. I would argue that cigarette addiction is both mental and physical.