Citizenship of the United States
A person who is considered a citizen by more than one nation has "dual citizenship". It is possible for a United States citizen to have dual citizenship; this can be achieved in various ways, such as by birth in the United States to a parent who is a citizen of a foreign country (or in certain circumstances the foreign nationality may be transmitted even by a grandparent) by birth in another country to a parent(s) who is/are a United States citizen/s, or by having parents who are citizens of different countries. Anyone who becomes a naturalized U.S. citizen is required to renounce any prior "allegiance" to other countries during the naturalization ceremony; however, this renunciation of allegiance renunciation of citizenship to those countries.
Iranian Americans
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. The Swiss government, acting through its embassy in Tehran, serves as protecting power for U.S. interests in Iran. The Iranian government does not recognize dual citizenship and will not allow the Swiss to provide protective services for U.S. citizens who are also Iranian nationals. The Iranian authorities make the determination of a dual national's Iranian citizenship without regard to personal wishes. In 2016, the U.S. Department of State warned U.S. citizens of the risks of travel to Iran. In some instances, foreigners, in particular dual nationals of Iran and Western countries including the United States, have been detained or prevented from leaving Iran.