U.S. remains optimistic on Iran sanctions

Iran said Monday it has military has launched war games to practice defending its nuclear sites, just as the U.N. began a new round of inspections of those same research and uranium-enrichment facilities.

CBS News correspondent David Martin reports that with no real expectation of a breakthrough, U.N. inspectors arrived in Tehran looking for answers to their questions about Iran's nuclear program. Among other things, the inspectors want to visit a military base where Iran is suspected of working on the science of a nuclear weapon.

"Importantly we hope that we can hope some concrete results after this trip. The highest priority remains of course the possible military dimensions of Iran's nuclear program," said inspection team chief Herman Nakaerts.

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Looming over inspections is the threat of Israeli air strikes to destroy Iran's nuclear facilities, which U.S. Defense Secretary Leon Panetta believes could come as early as this spring. In congressional testimony last week, Director of National Intelligence James Clapper testified that while Israel hasn't made that decision yet, spring would be a logical time.

"What could have given rise to this is simply the fact that the weather becomes better obviously in the spring and that could be conducive to an attack," Clapper said.

Clapper will be in Israel this week, the latest in a series of high level meetings in which U.S. officials have tried to persuade the Israelis to give sanctions more time to work. Although Panetta has said Iran could have a bomb as early as this year, Clapper testified it will take them longer than a year.

"That's, I think, technically feasible but practically not likely," Clapper said of the earlier timetable.

U.S. officials continue to believe Iran will abandon its nuclear ambitions if economic sanctions cause enough unrest to make the regime think it might lose its grip on power.