The White House said President Barack Obama was "deeply disappointed" by the conviction, while the journalist's father told a radio station his daughter was tricked into making incriminating statements by officials who told her they would free her if she did.
It was the first time Iran has found an American journalist guilty of espionage — a crime that can carry the death penalty.
Roxana Saberi, a 31-year-old dual American-Iranian citizen, was arrested in late January and initially accused of working without press credentials. But earlier this month, an Iranian judge leveled a far more serious allegation, charging her with spying for the United States.
The Fargo, North Dakota native had been living in Iran for six years and had worked as a freelance reporter for several news organizations including National Public Radio and the British Broadcasting Corp.
The journalist's Iranian-born father, Reza Saberi, told NPR that his daughter was convicted Wednesday, two days after she appeared before an Iranian court in an unusually swift one-day closed-door trial. The court waited until Saturday to announce its decision to the lawyers, he said.
Saberi's father is in Iran but was not allowed into the courtroom to see his daughter, who he described as "quite depressed." He said she denied the incriminating statements she made when she realized she had been tricked but "apparently in the case they didn't consider her denial."
Saberi's lawyer, Abdolsamad Khorramshahi, told The Associated Press he would "definitely appeal the verdict."
U.S. Secretary of State Hillary Rodham Clinton said the United States was working with Swiss diplomats in Iran to get details about the court's decision and to ensure Saberi's well-being. She said in a statement the United States will "vigorously raise our concerns" with the Iranian government.
The United States has called the charges against Saberi baseless, and the State Department said Thursday that Iran would gain U.S. good will if it "responded in a positive way" to the case.
Obama has said he wants to engage Iran in talks on its nuclear program and other issues — a departure from the tough talk of the Bush administration.
Iran has been mostly lukewarm to the overtures, but Iran's hard-line president gave the clearest signal yet on Wednesday that the Islamic Republic was also willing to start a new relationship with Washington.
In a speech, President Mahmoud Ahmadinejad said Iran was preparing new proposals aimed at breaking an impasse with the West over its nuclear program.
But Iran's judiciary is dominated by hard-liners, who some analysts say are trying to derail efforts to improve U.S.-Iran relations.
The United States severed diplomatic relations with Iran after its 1979 Islamic revolution and takeover of the U.S. Embassy in Tehran. Relations deteriorated further under the former President George W. Bush, who labeled Iran as part of the so-called "Axis of Evil" along with Saddam Hussein's Iraq and North Korea.
Saberi's conviction comes about two months ahead of key presidential elections in June that are pitting hard-liners against reformists who support better relations with the United States. Ahmadinejad is seeking re-election, but the hard-liner's popularity has waned as Iran's economy struggles with high-inflation and unemployment.
Some conservative Iranian lawmakers played down Saberi's conviction, saying the verdict would not affect any ongoing efforts to build trust between the United States and Iran.
"Although there is a wall of mistrust between Iran and the United States, the judicial verdict won't affect possible future talks between the two countries. The verdict is based on evidence," said lawmaker Hosseini Sobhaninia.
Saberi's father disagreed, telling NPR, "I don't think they have any evidence and I haven't heard any evidence that they have made public."
Human rights groups have repeatedly criticized Iran for arresting journalists and suppressing freedom of speech. The government has arrested several Iranian-Americans in the past few years, citing alleged attempts to overthrow its Islamic government through what it calls a "soft revolution." But they were never put on trial and were eventually released from prison.
"The Saberi case is the latest example of how Iranian authorities arbitrarily use spying charges to arrest journalists and tighten the gag on free expression," said Paris-based Reporters Without Borders.
Meanwhile, NPR said it was "deeply distressed by this harsh and unwarranted sentence."
Iran has released few details about the charges against Saberi. Iranian officials initially said she had been arrested for working in the Islamic Republic without press credentials, and she had told her father in a phone conversation that she was arrested after buying a bottle of wine.
An Iranian investigative judge involved in the case later told state TV that Saberi was passing classified information to U.S. intelligence services.
Her parents, who traveled to Iran from their home in Fargo in a bid to help win their daughter's release, could not be reached by the AP for comment on Saturday.
Saberi's father has said his daughter, who was Miss North Dakota in 1997, had been working on a book about the culture and people of Iran, and hoped to finish it and return to the United States this year.
Associated Press Writer James MacPherson in Bismarck, North Dakota contributed to this report.
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