WASHINGTON–Long-awaited talks are underway. Weapons inspectors are waiting in the wings, poised to return. Failing that, the probability of biting international economic sanctions against Iran's nuclear ambitions now is higher than ever.

But very quietly last week, even as U.S. President Barack Obama unexpectedly won the Nobel Peace Prize, the Pentagon won approval to speed up development of a sobering Plan C – a behemoth bunker-busting bomb designed to punch deeper and blow bigger than anything previously available in America's daunting military arsenal.

The so-called Massive Ordnance Penetrator (MOP) will weigh in at a whopping 13,600 kilograms, a nearly threefold increase over its predecessor and so heavy it will require a B-2 for delivery.

The Pentagon did not name Iran in citing an "urgent operational need" for the weapon. But military analysts see Tehran's nuclear facilities, including the newly disclosed and deeply buried installation near the city of Qom, as the prime impetus for a laser-guided bomb with a capacity to penetrate and plunder targets 60 metres underground.

U.S. Congress approved an additional $64 million for the procurement of four such MOPs, which, if dropped sequentially on the same co-ordinates, could alter a military equation that has long vexed U.S. and Israeli planners.

But the issue remains fraught with questions that even a bomb as big as this is unlikely to answer, experts on the Iranian file agree. And most categorize the new bomb as a remote, and thus far unproven, fallback plan that simply fills out the suite of options for a global effort to secure a peaceful compromise.

"The possibility of a military attack is not high, but anyone who thinks it is zero would be mistaken," said political analyst and author Meir Javedanfar, a Tel Aviv-based scholar born and raised in Iran. "The best hope remains that the Iranian leadership will see the peaceful deal that Obama is presenting: Iran can have nuclear energy and excellent relations with the West," said Javedanfar, director of www.middleeastanalyst.com.

"If they go the other way and decide to hunker down in the face of sanctions and continue to strive for a nuclear weapon, it will be terrible for the Iranian people. A few years from now the regime could resemble Pakistan – poor, unstable, isolated but having the bomb. And as we see in Pakistan, having a nuclear weapon does nothing for the people. This is not the legacy that the Iranian leaders want."

A ground war over the issue has never been more than an extremely remote possibility, not least because the U.S. has neither the blood nor the treasure to expend after nearly a decade of mobilization on the dual fronts of Iraq and Afghanistan. And military analysts are quick to point out that the new MOP bomb, even if it could reach its assigned target, would almost certainly destabilize the region in risky and unpredictable ways, with a more deeply isolated Iran in a position to retaliate by proxy, possibly by feeding insurgencies in the wars that flank its eastern and western borders.

Israel, which continues to cling to a strategy of nuclear ambiguity, neither confirming nor denying the existence of what is understood to be a fully developed nuclear weapons program, has lately tamped down talk of a pre-emptive strike against Iran. Analysts there say the latest developments, including an emerging international consensus for hard sanctions if soft diplomacy fails, has all but assured Israel will not act militarily on its own.

"It is now almost impossible for Israel to carry out military strikes against Iran without American consent," said Ephraim Kam, deputy head of the Jaffee Center for Strategic Studies at Tel Aviv University.

"Even in light of this new American bomb, which remains unproven and still under development, we are in a delicate moment where there is a growing international consensus toward the threat of harsh sanctions to persuade Iran the price of building a bomb is just too high," Kam told the Star.

"We should know by the end of the year how Iran intends to play this. But the bottom line (is) that the military option moves farther back as the chances of strong sanctions grow."

But in a conflict where big overtures and big threats go hand in hand, the development of bigger bombs are seen by many as inevitable, if only as a measure of additional deterrence.

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"All of these pieces are interconnected, from the building of international consensus for sanctions to the gathering of better intelligence on the ground to the development of new military options," said Javedanfar.

"The Bush era is behind us, and clearly the Americans no longer feel the only solution lies in threats and military force. But just as clearly, the Obama era will not be one where the Iranians can delay and delay indefinitely. There is a compromise on the table that I really hope comes together. In the next few months we should know."