Military action against Iran could have unintended consequences, Defense Secretary Leon Panetta said Thursday, sounding the administration's strongest reservations about a strike since the release of a new report on Tehran's escalating nuclear ambitions.
Panetta told Pentagon reporters that he agrees with earlier assessments that a strike would only set Iran's nuclear program back by three years at most.
"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 U.S. forces in the region," Panetta said.
The International Atomic Energy Agency said this week for the first time that Iran was suspected of conducting secret experiments whose sole purpose was the development of nuclear arms.
In response, the State Department said Thursday that the U.S. was looking at ways to increase economic pressure on Iran. Israeli leaders have said that without effective sanctions, they will not take any other options off the table.
Tehran, meanwhile, warned that any strike by the U.S. or Israel would trigger a strong response from Iranian forces. Iran insists it is pursuing nuclear energy for peaceful purposes.
Panetta, a former CIA director, said the IAEA report is in line with intelligence assessments that suggest Tehran is trying to develop its nuclear capabilities, but that there continues to be divisions within Iran over whether to build a bomb.
Asked what will happen if sanctions don't work, Panetta said, "I think our hope is that we don't reach that point and that Iran decides that it should join the international family." He said, however, that the U.S. agrees that military action ought to be the last resort.
State Department spokesman Mark Toner said the U.S. is consulting with international allies over what the next steps should be.
"Certainly we're going to look at ways that we can ramp up economic pressure on Iran," to persuade the Islamic republic to return to negotiations on its nuclear program and come clean about its intent, Toner said.
He added that all six countries that negotiate with Iran on nuclear issues _ the U.S., Britain, China, France, Germany and Russia _ "are united in their recognition that Iran's nuclear program raises ... serious questions that need to be addressed."
He said the United Nations already has put in place "very stringent" sanctions against Iran that are hampering the Iranian economy. But the U.S. still wanted those to be better enforced.
"We're going to look at unilateral actions as well," he added. "We're looking at the broad gamut of possibilities, how we can increase pressure on Iran."
Associated Press writers Robert Burns and Bradley Klapper contributed to this report.