The woman, identified as Afarin Mohajer, normally lives in Los Angeles and has been held in the women’s ward of Evin Prison, the group said.
Hengaw said security forces detained Mohajer on September 29 after she landed in Tehran and transferred her directly to Evin Prison, where she has had no access to due process and her legal status remains unclear.
US-based rights group the Human Rights Activists News Agency (HRANA) also reported her arrest, adding that there is no information about the charges against her.
“The Islamic Republic of Iran has a long record of detaining dual nationals and using them as leverage in foreign policy disputes,” Hengaw said.
“There are growing concerns that Mohajer may become the latest victim of this practice, often described as hostage diplomacy,” the rights group added.
More arrests
In August, The New York Times reported, citing rights groups and lawyers, that Iran is holding at least four Iranian–American citizens, including two individuals arrested after Iran’s June war with Israel.