A statement said the suspect was an officer of the Al-Quds Force, an elite unit of Iran's Revolutionary Guards. He was arrested in the Kurdish city of Al-Sulaymaniyah, in northern Iraq.
Al-Sulaymaniyah security chief Saif al-Den Ahmed said the Iranian was detained during a pre-dawn raid by U.S. troops on a hotel in the city. He was reportedly a member of an Iranian delegation staying at the hotel.
Iran protested the detention. The Foreign Ministry said the man was part of an official delegation that was invited by the authorities in Al-Sulaymaniyah.
Earlier this year, U.S. forces detained five Iranians in the Kurdish city of Irbil, accusing them of supporting militants.
Iran says the five -- who remain in custody -- are diplomats.
(compiled from agency reports)