President Barack Obama says he is "deeply concerned" for the safety of an imprisoned Iranian-American journalist in Iran.
He urged Tehran on Sunday to free Roxana Saberi, saying he was confident she was not involved in spying.
The president said he had "complete confidence" that she was not engaging "in any sort (of) espionage."
He said Washington would be in touch with Tehran about the case through Swiss intermediaries.
Ms Saberi, 31, was sentenced on Saturday to eight years in prison on charges of spying for the United States. Her trial began last Monday and lasted five days. No evidence was made public.
She was arrested in January for working in Iran after her press credentials expired. She was sentenced five days after going on trial on 13 April.
Ms Saberi has worked for the BBC, National Public Radio in the United States, Radio New Zealand and Fox News.
Presidential letter
Meanwhile, President Mahmoud Ahmadinejad has intervened in the case, saying Ms Saberi should be be dealt with fairly.
In a letter to the Tehran prosecutor, Mr Ahmadinejad said Ms Saberi should enjoy all her legal rights to defend herself when she appeals.
On Monday, the head of Iran's judiciary ordered a "quick and fair" appeal for Ms Saberi.
