WASHINGTON - Iranian authorities this week arrested the elderly father of an American jailed in Iran since October, the man's family said on social media on Wednesday.Siamak Namazi, a dual US-Iranian citizen, was detained by Iran's Islamic Revolutionary Guard Corps in October while in Iran visiting family. Officials have yet to announce charges against him.Baquer Namazi, Siamak's father, was arrested late on Monday in Tehran, his wife Effie Namazi said in a Facebook post on Wednesday. The 80-year-old Namazi, also a dual Iranian-American citizen, was taken to Evin Prison, where his son is also being held, she said.