From the U.S. State Department:
The Department of State warns U.S. citizens to carefully consider the risks of travel to Iran. Dual national Iranian-American citizens may encounter difficulty in departing Iran. U.S. citizens should stay current with media coverage of local events and carefully consider nonessential travel. ...
The U.S. government does not have diplomatic or consular relations with the Islamic Republic of Iran and therefore cannot provide protection or routine consular services to U.S. citizens in Iran.
U.S. State Department Warning