Ms Saberi has appealed against her sentence
An American-Iranian reporter jailed by Tehran for eight years on charges of espionage has gone on hunger strike, her father has said.
Reza Saberi said his daughter Roxana told him she had stopped eating five days ago.
"I'm very worried," he told Reuters news agency.
Ms Saberi was convicted of being an American spy and sentenced behind closed doors by the Revolutionary Court in Tehran a week ago.
She has become somewhat of a cause celebre, with US President Barack Obama expressing dismay at her conviction and rallies called to demand her release.
Mr Obama and Ms Saberi's family have insisted she is not a spy.
But Iranian President Mahmoud Ahmadinejad has refused to intervene, insisting the courts acted independently and that she will be accorded her full rights.
Ms Saberi has lodged an appeal, which Iranian authorities say will be heard fairly and quickly.