Roxana Saberi has been studying and working in Iran for six years
An Iranian-American journalist branded a US spy has been jailed for eight years by Iran after a brief trial held behind closed doors.
Roxana Saberi, 31, who was arrested in January and went on trial this week, denies the charge and plans to go on hunger strike, her father said.
Ms Saberi has reported for a number of foreign news organisations including the BBC, NPR radio and Fox News.
A spokesman said the US president was "deeply disappointed" at the outcome.
The journalist originally faced the less serious accusation of buying alcohol, and later of working as a journalist without a valid press card.
Then, in a period of fewer than two weeks, the charge of spying was introduced, and she was tried by the Revolutionary Court and sentenced.
No evidence of espionage was made public.
An unnamed judiciary official told the Iranian news agency Isna: "Branch 28 of the Revolutionary Court sentenced Roxana Saberi to eight years for espionage. She can appeal the sentence."
Ms Saberi's lawyer Abdolsamad Khorramshahi and her father confirmed that an appeal would be made.
The case is bound to have serious implications for relations between Iran and the US at a time when President Barack Obama has been reaching out to the Islamic Republic, the BBC's Jon Leyne reports from Tehran.
US Secretary of State Hillary Clinton said she was "deeply disappointed" by the verdict.
Washington, which has no diplomatic ties with Iran, was working with Swiss diplomats in Tehran to obtain details about the court's decision and ensure Ms Saberi's well-being, she said.
"We will continue to vigorously raise our concerns to the Iranian government," she added.
'Coerced and deceived'
Reza Saberi told NPR radio that his daughter was "weak and frail", and that interrogators had used undue pressure against his daughter to procure statements that were later used against her in court.
Ms Saberi's father (left) and lawyer say they are appealing
Her later repudiation of these statements was not considered by the court, he said.
His daughter was, he said, "not only coerced but deceived".
"They told her that if she says [something] like this, they will free her, and then they didn't free her. Later she found out that it was a trick."
Mr Saberi said his daughter was "quite depressed" and wanted to go on hunger strike but he was trying to persuade her against doing so.
Roxana was tried in secret and no evidence of espionage has been made public
Mr Saberi, who was not allowed to attend the trial, said his daughter's lawyer had not been allowed to argue the case for the defence properly.
Expressing his dismay at the verdict, he added that he had been hoping for a sentence of six months and clemency.
"We are extremely concerned at the severe sentence passed on Roxana Saberi," the BBC Press Office said.
"Roxana was tried in secret and no evidence of espionage has been made public. Roxana's many friends in the BBC are saddened by the decision and are thinking of Roxana and her family at this difficult time."
NPR's chief executive, Vivian Schiller, said: "We are deeply distressed by this harsh and unwarranted sentence."
This is a very tough sentence, even for the serious charge of spying, our correspondent says.
Iran's authorities have not even given details of the charges against her, he notes.
The conviction was criticised by the New York-based Committee to Protect Journalists, which said her trial had "lacked transparency".
"We call on the Iranian authorities to release her on bail pending her appeal," said Mohamed Abdel Dayem, the group's Middle East and North Africa programme coordinator.
Public awareness of Ms Saberi's situation is low in Iran, where local media do not seem to have reported her arrest or trial in any way, our correspondent says.
A US-Iranian national, Ms Saberi has spent six years in Iran studying and writing a book.
The daughter of an Iranian father and a Japanese mother, she was once crowned Miss North Dakota and was among the top 10 finalists in Miss America 1998.
She holds two master's degrees, from Northwestern University in the US and from Cambridge University in the UK.
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