MARGARET WARNER: More sanctions, more rhetoric and the risks of war between the U.S. and Iran.
From Iran's naval exercises, to its latest nuclear announcement, to new sanctions by the U.S., tensions are on the rise. Today, Tehran claimed Ayatollah Ali Khamenei, the country's supreme leader, had received a letter from President Obama containing threats and an offer of new talks.
In Washington, White House spokesman Jay Carney neither confirmed nor denied the claim.
JAY CARNEY, White House press secretary: Our position has not changed. We -- any communications we may have had with or may have with the Iranians are the same in private as they have been in public.
MARGARET WARNER: Lately, much of that communication has consisted of saber-rattling, like Iranian naval maneuvers. And after President Obama signed legislation late last month to isolate Iran's Central Bank, which collects payments for its oil exports, the country's military leaders threatened to block oil shipments through the Strait of Hormuz.
One-fifth of the world's oil production flows through the strait. Iran's news agency said today the first part of the Obama letter warned that closing the strait was Washington's red line.
U.S. Defense Secretary Leon Panetta said as much today, leaving open both diplomatic and military options.
SECRETARY OF DEFENSE LEON PANETTA: We have always made clear what our policies are there with regards to Iran, both in terms of their not obtaining a nuclear weapon and also obviously not closing the Straits of Hormuz. It takes two to be able to engage. And we have always expressed a willingness to try and do that.
But we have always made clear that in terms of any threats to the region, in terms of some of the behavior that they have conducted in the region, that we will also be prepared to respond militarily if we have to.
MARGARET WARNER: Iran has been showing off its own determination, test-firing a new longer-range cruise missile in the Gulf and announcing it had begun enriching uranium at a second underground site.
Back in the U.S., many Republican presidential candidates have been vowing they'd be even tougher with Tehran.
Former Sen. Rick Santorum spoke on NBC's "Meet the Press."
RICK SANTORUM (R): And I would be saying to the Iranians, you either open up those facilities, you begin to dismantle them and -- and make them available to inspectors, or we will degrade those facilities through airstrikes, and make it very public that we are doing that.
MARGARET WARNER: Adding further to the debate about the advisability or danger of outright war with Iran, a flurry of dueling opinion pieces in leading foreign affairs publications, some advocating a military strike against Iran's nuclear program sooner rather than later, and others warning against the prospect.
And yesterday, longtime analyst Leslie Gelb, writing in The Daily Beast, warned that "America is once again stumbling toward war."
For now, Secretary Panetta says the U.S. military is taking no special steps to prepare for conflict or crisis with Iran, because American forces in the region are already fully prepared.