Germany's Foreign Ministry has confirmed the arrest of a German national in Iran for allegedly taking pictures in "prohibited areas."
The ministry declined to provide further details, but sources told RFE/RL's Radio Farda that the 66-year-old male has been in prison in Iran for more than a month.
The sources added that the man was arrested more than 40 days ago and has spent half of his time in custody in solitary confinement. He is now imprisoned in the general ward of Aran and Bidgol prison near the Iranian central city of Kashan, they said.
The man reportedly visited several cities as he toured Iran on a motorcycle, including Tehran and Tabriz.
German authorities only found out about his arrest after he lost contact with his family, which prompted them to seek help from the German Embassy in Iran.
The German Foreign Ministry said its mission in Tehran has had access to the man, but further details could not be disclosed.
Iranian judicial and security authorities have yet to announce the arrest of the German citizen.
Two Iranian-German dual citizens, Jamshid Sharmahd and Nahid Taghvi, were already being held in Iran, which has arrested dozens of foreigners and dual nationals in recent years, often on widely criticized espionage and security-related charges.
Western countries have repeatedly charged that Iran is trying to take advantage of foreign countries by taking dual and foreign nationals hostage.
The arrest of the German national also comes as Iran and world powers are reportedly about to reach agreement on reviving the 2015 deal over Tehran's nuclear program.