Reza Saberi has told the Associated Press that "she went on a hunger strike Tuesday to protest her imprisonment. Today is the fifth day."
He added Saturday that his daughter Roxana Saberi will remain on a hunger strike "until she is freed."
The 31-year-old dual American-Iranian citizen was sentenced to eight years in prison just days after she was tried behind closed doors earlier this month.
Saberi was arrested in late January and initially accused of working without press credentials. But earlier this month, an Iranian judge charged her with spying for the United States.