People who wish to enter the U.S. as nonimmigrants are often allowed to apply for their visas at any U.S. embassy or consulate; although doing so might not always be recommended. By contrast, those who wish to enter the country as new permanent residents are usually required to obtain an immigrant visa at a U.S. embassy or consulate in their country of citizenship or last residence. This requirement may pose a difficulty to citizens of countries where the U.S. has no diplomatic presence, or where the U.S. diplomatic mission has limited or suspended its activities. This can happen due to diplomatic issues, security concerns, natural disasters, geographic convenience, or other reasons.
Fortunately, the U.S. State Department (the agency that oversees U.S visa processes) can accommodate immigrant-visa seekers from such countries, typically by processing their applications at U.S. embassies or consulates in neighboring states (although limited in-country services might still be provided, sometimes through third-country embassies).
Less fortunately, however, this type of accommodation often entails additional barriers related to travel. This might include visa requirements for access to host states as well as costs of transportation and extended stays on foreign land.
The State Department sometimes also maintains special websites as "virtual" diplomatic missions to countries or territories where it has no physical posts. These websites often provide valuable information for prospective visa applicants. Nevertheless, they do not usually enable remote visa services, or otherwise substitute for actual embassies or consulates.
The U.S. typically extends diplomatic relations to countries whose "sovereignty" it legally recognizes, and withholds diplomatic presence from territories with which it does not enjoy normal diplomatic relations. There are important exceptions, however.
In 2015, the U.S. government began reestablishing direct diplomatic relations with Cuba, although for many years an indirect presence (an "Interests Section") had been maintained in the country's capital through the Swiss Embassy.
A few other countries still hold no official diplomatic relationship with the United States, including Bhutan, Iran, and North Korea. Citizens of all three countries have nonetheless been allowed to process their U.S. immigrant visa applications in nearby countries: India for citizens of Bhutan; Turkey, the United Arab Emirates, and Armenia for citizens of Iran; and China for citizens of North Korea.
So, for example, immigrant-visa seekers from Iran would need not only to appear for an interview but also to complete other application-related requirements (such as a medical examination) in one of the three designated countries. (Note that each post may impose very different scheduling procedures when it comes to interviews for nonimmigrant visas.)
The U.S. government sometimes maintains consulates in territories that it does not, for one reason or another, formally recognize as sovereign. This has been the case, for example, in the city of Jerusalem. In other cases, a virtual presence may be maintained without a physical post, as in the case of the U.S. Virtual Consulate in Gaza, which has served as a platform for outreach to the Palestinian territory. (Palestinians who remained stateless could process their immigrant visa applications at the U.S. Consulate General in Jerusalem.)
There are also contested territories where the U.S. has created special organizations to provide consular and other quasi-diplomatic services. This has been the case, for example, in Taiwan; an island claimed by China and no longer officially recognized as independent by the U.S. after 1979. The U.S. has nonetheless continued after that date to offer visa services inside the territory through a special not-for-profit organization: the American Institute in Taiwan.
There are countries that enjoy full diplomatic relations with the U.S., but where, mainly for reasons of geographic convenience, the U.S. does not maintain any diplomatic presence. These include the African state of Guinea-Bissau, Grenada, Saint Lucia, and other small Caribbean islands.
Residents of these nations are advised to apply for their immigrant visas at U.S. embassies in designated nearby countries: Senegal for Guinea-Bissau, and Barbados for the Caribbean islands.
Finally, there are countries where the U.S. has an official diplomatic presence but also where, due to country and international conditions (insecurity, political conflict, or natural disasters), visa services have been suspended or limited.
For example, immigrant-visa seekers from Yemen are likely to be scheduled to appear for their interview at the U.S. embassy in Egypt. This can be inconvenient, because Yemenis need a visa to enter Egypt. (In some cases, the U.S. government has accepted requests for case transfers to Djibouti and other nations.)
Similarly, applicants from Libya have recently been processed at the U.S. Consulate in Tunisia, applicants from Syria have been processed at the U.S. embassy in Jordan, and applicants from Somalia have been processed at the U.S. embassies in Kenya, Jordan, and Djibouti.
See the U.S. State Department website for a list of consulates and embassies serving each country, and visit the website of the U.S. consulate (or virtual consulate) serving your country for further information.