In response to Decaf's comment:
I also did the program and am now on a leave of absence after the first year for personal reasons. It's true that studying in Iran has many frustrations, but not necessarily the ones Decaf describes. The program is indeed heavy on IR, emphasizing Iran's own revisionist perspective on global politics. In terms of coursework quality, it's really a mixed bag. Some courses (like an elective on Iran's political economy) are quite rewarding. There is lots of room for independent study. It can be quite intellectually stimulating, provided you're persistent and willing to work on your own and not just motivated by assignments and grading, which is generally quite lax. The program provides a decidedly "insider" view of Iran, so it's useful to have some background in the field to be able to evaluate things critically and read between the lines. I wouldn't recommend it to someone who's just looking for an easy, affordable, exotic-sounding Master's degree.
There are some courses that are basic and introductory, more in the spirit of a 100-level undergraduate lecture than a graduate seminar, and their usefulness varies with how familiar you already are with the given topic. The main cause of frustrations had to do with bureaucracy and the general academic atmosphere. (But then again, I assume that if you're considering this program, you know that Tehran Univ is no UC Berkley...) Many of my classmates had negative experiences with student housing, and had to live in hotels for the first days or weeks. The university doesn't have very many mechanisms for helping out lost foreign students, so it is generally recommended to enlist a local to help you get set up, especially if your Persian isn't top-notch.
On the U.S. citizen question: You can be a dual citizen and study here, but in three years I haven't met anyone at the univ or the Dehkhoda institute who had gotten in on a U.S. passport. That may be changing as the US Treasury lifts sanctions on academic exchange, so it's best to contact the department directly.
