Gathered around conference tables in Vienna, diplomats are working feverishly to hammer out the terms of a long-elusive nuclear deal with Iran.
The official deadline for an agreement is Tuesday, but the parties have all but declared that talks will not be concluded by the stroke of midnight. Though the negotiations are likely to continue for at least several more days in search of an agreement, the remaining obstacles and dragging timeline are raising questions about whether a deal will be reached.
Even as officials from the United States and its allies emphasize their commitment to the diplomatic process, there’s a heightened awareness that failure to reach a deal could increase the pressure for U.S. military action against Iranian nuclear sites.
In an interview in April, Defense Secretary Ashton Carter told CNN’s Erin Burnett that while the U.S. is focused on the talks, it is also prepared to invoke the military option if they fall through.
“We have the capability to shut down, set back and destroy the Iranian nuclear program and I believe the Iranians know that and understand that,” Carter said.
Critical to that capability is the powerful ground-penetrating bomb known as the Massive Ordnance Penetrator (MOP) – a 15-ton behemoth that can explode 200 feet underground and is designed specifically to destroy deeply buried and fortified targets.
The MOP is the weapon of choice for underground sites such as the ones at Fordow and Natanz in Iran, which house some of that country’s largest nuclear reactors.
And the bomb is ready for use if needed, Carter said.
A deterrent now, or in the future
Even if a deal is reached this week, the military’s contingency plans could act as a further deterrent. Iran has a history of conducting nuclear work in secret, and many in the international community question whether its government can be trusted to fully roll back the military dimensions of the nuclear program.
The very existence of the site at Fordow, buried deep under a mountain near the city of Qom, was kept hidden from the international community until 2009.
And Iran’s reluctance to provide international inspectors access to nuclear sites remains a sticking point in the talks, particularly after Iran’s Supreme Leader, Ayatollah Ali Khamenei, was quoted by Iran’s official state news agency last month as saying his country would not allow inspectors into military facilities.
This could keep inspectors from the UN nuclear watchdog, the International Atomic Energy Agency, out of facilities like Parchin, where Iran is believed to be conducting high explosives testing.
The U.S. military already maintains targeting folders on thousands of sites around the world, including all known Iranian nuclear sites.
Plans for these sites include detailed analysis of target structure, geology, proximity to civilian populations, air defense and potential risk.
Risks in an attack
There are also vulnerabilities. The military would have to determine how many bombs to drop in order to guarantee each site’s destruction; the more sorties required, the easier it is to lose the element of surprise.
Iran also maintains significant coastal air defenses, which would have to be successfully jammed.
At a congressional hearing last week, Carter told lawmakers he has a “responsibility to make sure that the military option is real.”
“It’s not part of the negotiation,” he said, “but it’s a very, very big role, and we take it very seriously.”
Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey added that he is in active consultations with regional allies, including Israel.
“If there’s a deal,” Dempsey said, “I’ve got work to do with them. And if there’s not a deal, I’ve got work to do with them.”
He added, “We’re committed to doing that work.”
Israeli military action?
Israeli Prime Minister Benjamin Netanyahu has been one of the most vocal critics of the negotiations with Iran and has vowed that Israel will act alone if necessary to stop Tehran from getting a nuclear weapon.
But the Israelis are more limited than the United States in their military capabilities.
Absent U.S. involvement, they would have to rely heavily on non-stealth F-15s, which would need to be re-fueled en route to their targets in Iran.
They also lack the kind of bombs that can reach the low depths of the Massive Ordinance Penetrator, presumably putting sites like Fordow and Natanz out of reach.
Israel also risks incurring the ire of the international community if it acts alone.
And any military strike is unlikely to end Iran’s nuclear efforts. As President Barack Obama told Israel’s Channel 2 in May: “A military solution will not fix it, even if the United States participates. It would temporarily slow down an Iranian nuclear program, but it will not eliminate it.”
CNN’s Deena Zaru, Jeremy Diamond and Don Melvin contributed to this report.