The United Nations' children agency says it hopes an Iranian-American held in Tehran "will be reunited soon with his wife and loved ones."
The UNICEF appeal is on behalf of 80-year-old Baquer Namazi, who was detained in late February returning to Tehran. His son, Siamak Namazi, has been detained since October in Iran.
The UNICEF appeal, issued Thursday, noted the elder Namazi's work with UNICEF. He also once served as governor of Iran's oil-rich Khuzestan province under the U.S.-backed Shah Mohammad Reza Pahlavi.
The Namazi family fled Iran after the 1979 Islamic Revolution, but appears to have kept business ties in Iran. The younger Namazi traveled back several times before his arrest.
Their detentions come after the Iran nuclear deal and a prisoner swap between Iran and the U.S.