Do sanctions against a country apply to its dual nationals or US residents?

Yes. OFAC’s “U.S. person” definition, applied consistently across every sanctions program under the International Emergency Economic Powers Act (50 U.S.C. §§ 1701–1706), covers U.S. citizens and lawful permanent residents (green card holders) wherever they are physically located, including dual nationals, plus anyone physically present in the United States regardless of nationality. A U.S.-Iranian dual national living in Tehran remains bound by the Iranian Transactions and Sanctions Regulations (31 CFR Part 560); a U.S. citizen residing in Moscow remains bound by the Russian Harmful Foreign Activities Sanctions Regulations (31 CFR Part 587). The definition also reaches entities organized under U.S. law, including their foreign branches, and — for Cuba and Iran specifically — foreign entities that a U.S. person owns or controls by 50% or more. Non-U.S. persons without any U.S. nexus generally fall outside primary sanctions but can still face secondary-sanctions exposure.