Mr Saberi and his wife live in the US, but have been in Tehran since Sunday
The father of a detained Iranian-American journalist accused of spying in Iran says he will not leave Tehran until she is released from prison.
"I demand they release my daughter as soon as possible," Reza Saberi said in an interview with AP Television News. "I will stay here until she is freed."
Roxana Saberi is being held in Evin prison near Tehran. She is due to appear in court next week.
US Secretary of State Hillary Clinton has also appealed for her release.
'Thin and weak'
Ms Saberi's parents arrived in Tehran at the weekend from their home in Fargo, North Dakota, where she grew up.
They were allowed to see her for 20 minutes.
Ms Saberi has been living in Iran for the last six years
"She was spiritually better than before," Mr Saberi told AP news agency. "However, she was physically extremely thin and weak, but she said she eats now and is going to exercise.
"This gave us the hope that she will become better," he added.
Ms Saberi originally faced the less serious accusations of buying alcohol and working without a valid press card.
The journalist, 31, worked briefly for the BBC three years ago. She has also worked for the American public radio network NPR and the TV network Fox News.
Ms Saberi's father said he could not comment on the accusation of spying under advice from her lawyer.
He said she was definitely a dual citizen, after an Iranian judge said they could not confirm her US nationality.
A number of UK and US media outlets, including the BBC, have called on Iran to allow independent access to her.