State Department deputy spokesman Tom Casey said Washington is seeking consular access for Ali Shakeri -- a peace activist who was supposed to have left Iran to fly to Europe on May 13.
Shakeri is the third Iranian-American detained in Iran in recent weeks.
The other two are Haleh Esfandiari, the head of the Middle East Program at the Washington-based Woodrow Wilson Institute, and Kian Tajbakhsh, a consultant with the Open Society Institute. Both have been charged with endangering Iranian national security through propaganda against the system and espionage for foreigners.
Authorities have meanwhile prevented Prague-based Radio Farda journalist Parnaz Azima from leaving the country, and announced a charge of acting against Iranian national security against her.
They are also blocking the departure of French-Iranian journalism student Mehrnoush Solouki.