The United States has called for the release of two Iranian-American citizens detained without charge in Tehran.
Family members say businessman Siamak Namazi was arrested in October while his father Baquer, 80, was detained last month. Both men are believed to be in Tehran's notorious Evin prison.
"We're deeply concerned about reports of the detention of U.S. citizens Siamak Namazi and Baquer Namazi in Iran," State Department spokesman John Kirby said on March 18.
"We're not aware of any charges against either man, and we believe that both reported detentions are unjust," he said.
"We call on Iran to allow consular access via Swiss authorities and to release both men as soon as possible so they can return to their families."
Friends describe Siamak Namazi as a businessman who was not involved in politics except for a time when he lobbied Washington to end a U.S. embargo on selling medicines to Iran.
Baquer Namazi is a retired UNICEF official.