The nation's top military officer, Gen. Martin Dempsey, is in Israel where he's expected to send a clear message: Don't attack Iran, and let the tougher sanctions take hold.
Dempsey's trip to Israel was scheduled weeks ago, but it comes at a particularly sensitive time. Iran has threatened to close the Strait of Hormuz, the key route for oil shipments, and has stepped up its naval activities.
An Iranian nuclear scientist was recently killed by a drive-by assassin, and Iran is blaming Israel.
President Obama has called Israeli Prime Minister Benjamin Netanyahu about what aides call "Iran-related developments."
"This is getting very dangerous," says Jon Alterman, a former State Department official who runs the Middle East Program at the Center for Strategic and International Studies. "All the senior people I know in the U.S. government are starting to lose sleep over where this all might go."
The greatest concern for U.S. officials is an Israeli attack on Iran's nuclear facilities — which Iran insists are only for peaceful purposes. An Israeli attack, said one Pentagon official, could result in what he called blowback: Iranian agents striking U.S. military and diplomatic personnel throughout the Middle East.
Some U.S. officials believe that an Israeli attack is more likely now, because Iran appears to be stepping up its nuclear program — even hiding portions of it deep inside a mountain.
In addition, the U.S. military has left Iraq and no longer controls Iraqi airspace. Israeli warplanes could fly virtually directly across Iraq — even without Iraq's permission — to bomb Iranian nuclear sites.
Israel Says No Decision Made
Israeli Defense Minister Ehud Barak has downplayed the talk of an imminent attack.
"We haven't made any decision to do this. The entire thing is very, very far off," Barak told Israel's Army Radio this week.
Gawdat Bahgat, a Middle East expert at National Defense University, thinks Israel will strike if it sees Iran's nuclear program progressing past a certain point.
"I believe Israeli has its own red line, and if Iran crosses this red line, Israel will attack," he says.
The sense among experts is that Israeli officials are debating where that red line is. There's disagreement about what milestones would warrant airstrikes by Israel.
"I don't think the Israelis know what their intention is," says Alterman, the former State Department official. "I think they genuinely haven't made a decision. I think when they do make a decision, I don't think it's a decision they would share widely."
Would Israel inform the U.S. in advance of a military strike on Iran?
"My guess is the Israelis would probably have to give the United States at least some minutes warning, but probably not much more than that," says Alterman.
Alterman and other analysts say Israel views a nuclear-armed Iran as a threat to its existence. But at least for the time being, Israel seems willing to wait and see if tougher sanctions work.
Americans Stressing Sanctions
American officials, for their part, are continuing to push for non-military pressure on Iran's nuclear program.
"The responsible thing to do right now is to keep putting diplomatic and economic pressure on them to force them to do the right thing," Defense Secretary Leon Panetta told CBS's Face the Nation last week. "And to make sure they do not make the decision to proceed with the development of a nuclear weapon."
Yet, Panetta says that no option is off the table, even a military one. On the same program, Dempsey was asked if the U.S. could destroy Iran's nuclear program.
"Well, I certainly want them to believe that that's the case," he said.
Dempsey went on to say that his job is to plan for all military options. But the case he's making in Israel is to hold off on any military action.
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