The U.S. Defense Secretary Leon Panetta said Thursday, November 10, a military strike against Iran could have "unintended consequences".
He said it would only delay Iran's nuclear efforts by three years at most.
Correspondents say the comments appear to play down speculation that a military strike might be used to cripple Tehran's nuclear program.
On Tuesday, the UN's nuclear watchdog, the IAEA, said Iran was carrying out research aimed at developing nuclear weapons capacity.
"You've got to be careful of unintended consequences here," Mr Panetta told reporters in Washington, when asked about his concerns about a military strike.
He acknowledged military action might fail to deter Iran "from what they want to do". "But more importantly, it could have a serious impact in the region, and it could have a serious impact on U.S. forces in the region," he said. "And I think all of those things need to be carefully considered."
Mr Panetta said he supports the use of "the toughest sanctions – economic, diplomatic pressures – on Iran to change their behavior".
Asked what the U.S. would do if sanctions did not force Iran to change course, he said the hope was that it would not reach that point, BBC reported.
