Iranian authorities have arrested the 80-year-old father of an Iranian-American citizen who's been in jail in Iran since October, the family said in a Facebook post.
Baqer Namazi, the father of Siamak Namazi, was arrested on February 22 and taken to Tehran's Evin prison, his wife, Effie Namazi, wrote on Facebook.
Namazi's son, Siamak, is also being held at the notorious prison.
"We are aware of reports that a U.S. citizen was detained in Iran," State Department spokesman Mark Toner said in a short statement e-mailed to RFE/RL.
"The U.S. Department of State has no higher priority than the protection of U.S. citizens overseas," the statement said.
"Due to privacy considerations we have no further information at this time."
The reason for their arrest and the charges against them is unclear.
Siamak Namazi was arrested by the intelligence unit of the Islamic Revolutionary Guards Corps (IRGC).
The IRGC has arrested a number of journalists and activists in recent months.
With reporting by Reuters