Persons with Potential Rights to Citizenship
Persons born in countries other than the United States may have a claim, under U.S. law, to United States nationality if:
With few exceptions, a person born in the United States has a claim to United States citizenship. Any applicant believing that he or she may have claim to United States citizenship should not apply for a visa until his or her citizenship has been determined. The applicant should inform the consular officer immediately of a potential qualification for a U.S. passport rather than an immigrant visa. For further information on this issue, please contact the American Citizen Services (ACS) Citizenship Issues section.
For more general information regarding Immigrant Visas please go to: http://travel.state.gov/visa/immigrants.html