US Defence Secretary Leon Panetta warned Thursday that an attack on Iran to stop its nuclear programme could have "unintended consequences", dpa reported.
"You've got to be careful of unintended consequences here. And those consequences could involve not only not really deterring 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 US forces in the region," he told reporters.
Panetta agreed with assessments - by his predecessor, Robert Gates, and former chairman of the Joint Chiefs of Staff Admiral Mike Mullen - that bombing Iran's nuclear facilities would set back its programme by at most three years.
The International Atomic Energy Agency released a report this week that provided the clearest indications yet that Iran has been developing nuclear arms, detailing a large number of nuclear-related projects and experiments, some of which might be ongoing.
The US has called the news "alarming" and said it was consulting with its allies on how to further pressure Tehran.
Iran, which maintains its nuclear programme is for peaceful purposes, has vowed to press on despite the highly critical report.
Panetta said military action ought to be a last resort and that concerns by the US and Israel about the Iranian nuclear efforts make it important that "we apply the toughest sanctions, economic, diplomatic pressures on Iran to change their behaviour."