U.S. Secretary of State Hillary Clinton has expressed concern about the health of Iranian-American journalist Roxana Saberi, who is imprisoned in Iran. In an appearance before a Senate panel, Clinton said Tehran is sending mixed signals about Saberi's fate.

Secretary Clinton renewed U.S. calls for Iran to release Roxana Saberi, who was sentenced to eight years in prison by Iran for spying, charges the United States says are baseless.

"We have great concerns about Ms. Saberi's health and well being. She has arbitrarily, in our view, been held without any kind of transparency and process," said Clinton. "We have called on the Iranian government, both directly and through other emissaries, to release her."

Saberi's father says she has been on a hunger strike for more than a week to protest her incarceration. Tehran denies she has taken such action.

Clinton said the United States is appealing to Iran through public and private channels.

"We hear mixed responses all the time from the [Iranian] government. They are going to let her out; they are going to let her out in two months," she said. "They are going to sentence her to eight years; they are going to do an appeal. I think it shows you how difficult it is to deal with this government in Iran because they are impervious to the human rights and the civilized standards that one should apply."

Appearing with Secretary Clinton before the Senate Appropriations Committee was Defense Secretary Robert Gates, who again argued the best way to press Tehran to abandon its nuclear weapons program is diplomatically, not militarily.

"Even a military attack will only buy us time and send the program deeper and more covert. How do we get them to decide it is not in their interest to pursue nuclear weapons? It seems partly it is economic pressures, partly it is diplomatic isolation, partly it is seeing their neighbors band together to collaborate on air and missile defense that is aimed only at Iran," said Gates.

Gates said the United States should pursue a partnership with Russia on missile defense in Europe to further isolate Iran.

He said that it is also important to persuade Iran its security interests are poorly served by having nuclear weapons, because it will spark a nuclear arms race in the Middle East.

Secretaries Gates and Clinton agreed the United States should work with its allies on tougher international sanctions against Iran.

The two officials appeared before the Senate Appropriations Committee to discuss President Barack Obama's request for $83.4 billion for the wars in Iraq and Afghanistan, and aid to Pakistan.