Mr Saberi says he has been kept in the dark on Roxana's whereabouts
Iran has confirmed that it is holding an Iranian-American journalist, Roxana Saberi, in a Tehran prison.
An Iranian judiciary spokesman said she had been arrested on the orders of the revolutionary court, but he did not know what the charges were.
The foreign ministry said on Monday Ms Saberi had been detained for working illegally as a journalist.
Ms Saberi, 31, worked briefly for the BBC three years ago, before her Iranian press credentials were revoked.
Ms Saberi has also worked for the American public radio network NPR and the TV network Fox News.
Speaking from his home in North Dakota, her Iranian-born father Reza Saberi said a lawyer would be sent to Tehran's Evin prison.
"We have been very anxious and worried because they kept us completely in the dark," Mr Saberi said.
She was reportedly arrested in late January and had been allowed to call home only on 10 February, when she told her father she had been arrested for allegedly buying alcohol.
Ms Saberi worked for the BBC for a few months in 2006
"We are happy that at least they are acknowledging she is in the prison," Mr Saberi said in comments quoted by AFP.
"We want a fair trial... They are accusing her of nothing," he added.
Ms Saberi has both Iranian and US citizenship, although the Iranian authorities do not recognise dual nationality and are believed to be treating her as one of their own nationals.
NPR reportedly acknowledged that Ms Saberi's press credentials had been revoked but the authorities had continued to allow her to report short news stories.
Iran and the US have not had diplomatic ties since 1979. Their relations are generally strained, with differences particularly sharp over Iran's nuclear programme and the US military involvement in the Middle East.