The Iranian-American journalist who was sentenced to eight years in prison for spying has gone on a hunger strike, her father said Saturday.

Roxana Saberi poses for a photograph in Bam, 1,250 kilometres southeast of Tehran, in March 2004. (Reuters)

Roxana Saberi, 31, is on her fifth day of the fast, Reza Saberi said.

He said she will go without food until she is freed.

Last Monday, Mahmoud Hashemi-Shahrudi, the head of the Iranian judiciary, ordered Saberi's appeal of the sentence to be heard “quickly and fairly.”

His comments came a day after Iranian President Mahmoud Ahmadinejad intervened in the case and urged Tehran’s chief prosecutor to allow Saberi to defend herself.

Saberi was sentenced after a one-day trial held behind closed doors earlier this month.

She was arrested in late January and taken to Tehran's Evin prison. Initially, she was accused of working without press credentials, but earlier this month, an Iranian judge charged her with spying for the United States.

Her parents have travelled to Iran from their home in Fargo, N.D., in a bid to help win their daughter's release.

With files from The Associated Press