The West’s confrontation over Iran’s nuclear program is heating up — yet again.

This week, Iranian negotiators will square off with the (bureaucratically-dubbed) P5+1 — the five permanent UN Security Council members, plus Germany. They’ll meet in Almaty, Kazakhstan.

The stakes are getting higher, and the pressure is building.

In recent months, the world has imposed unprecedented sanctions on Iran, and its economy has been battered as a result. In response, Iran has threatened to disrupt tanker traffic in the Straits of Hormuz, a strategic chokepoint through which about one-fifth of the world’s oil flows.

Meanwhile, Israeli Prime Minister Benjamin Netanyahu has grown increasingly impatient. Last fall he demanded that President Barack Obama declare “red lines” that it would not let Iran cross. Naysayers have dismissed some of Netanyahu’s hawkish rhetoric as political posturing, ahead of the January 2013 elections. But no one disputes that an Iranian nuclear weapon would pose an existential threat to Israel. Netanyahu insists that the world must act before Iran has sufficient nuclear material for bomb, a milestone that it could reach this year, barring intervention.

So the prospect of military action — a move that could destabilize the Middle East — can’t be ruled out.

State-side, most Americans say they would support the Obama administration if it decided to use force to prevent Iran from getting nukes. The US has built a 30,000-pound "bunker-buster" bomb called the Massive Ordnance Penetrator, meant for nuclear sites, and is now working on a bigger bomb needed to destroy Iran’s most durable installations.

UPDATE: On Wednesday Feb. 27, talks ended with an agreement to convene each side's nuclear experts in Istanbul in March 18, followed by more high level negotiations in Almaty on April 5-6. Iran's negotiator commented that "world leaders are taking a 'more realistic approach,' to the Iranian nuclear standoff," AFP reported. However, there was no evidence that Iran would accomodate the P5+1's demands, and the only identifiable accomplishment was the agreement to keep talking.

The confrontation boils down to this: Iran claims its rapidly advancing nuclear program is solely civilian; the West accuses it of pursuing technology that would eventually enable it to build nuclear weapons — and its evidence is strong.

The details get arcane quickly, but the current controversy centers mainly on centrifuges and the enriched uranium they produce. At lower levels, there are legitimate non-military uses for enriched uranium. It can power nuclear reactors (enriched at a level of 3 to 5 percent uranium-235), or be used for medical and research purposes (20 percent), or for making bombs (90 percent). The same centrifuge technology — albeit at different intensity — is used for each level of enrichment.

Iran admits that it is producing 20 percent enriched uranium, for the Tehran Research Reactor, which has been operational since 1967.

Legitimate concerns arise because that 20-percent-enriched fuel is dangerously close to what is needed to produce a nuclear weapon.

As the Congressional Research Service noted in October 2012 “little additional effort [beyond the 20 percent level] would be required to use this uranium to produce weapons-grade enriched uranium.” While there are additional hurdles to producing a viable nuclear weapon, obtaining this weapons-grade uranium is widely seen as the biggest challenge.

Iran’s claims to have legitimate national interest in enriching uranium don’t necessarily hold up. The international community has long urged Iran to purchase nuclear fuel from other countries; Indeed, its research reactor now runs on Argentine fuel. This would obviate Iran’s need for the centrifuges that can be used to create weapons material. Still, Iran has insisted on enriching the fuel itself, claiming this is needed as a safeguard against possible fuel supply disruptions.

So how close is Iran to actually having a nuclear weapon? That’s a big question, without a reliable answer. Here’s what we know: The US government’s 2007 National Intelligence Estimate indicated that although Iran had exerted “considerable effort from at least the late 1980s to 2003 to develop such weapons,” it appeared to have halted actual weapons-building efforts (but not enrichment) in 2003, in response to international pressure.

However, the classified 2010 version of the intelligence estimate found, according to the Washington Post, that Iran had resumed "early stage research and development work on aspects of the manufacturing process for a nuclear weapon." And National Intelligence Director James R. Clapper told the Senate Select Committee on Intelligence in February last year, “They are certainly moving on that path, but we don’t believe they have actually made the decision to go ahead with a nuclear weapon.”

If Iran decides to resume building a nuke in earnest, the project could be completed in relatively short time, but not overnight. In January 2012, Defense Secretary Leon Panetta stated that Iran would “need about a year” to produce a nuclear weapon, and “possibly another two years” to incorporate it into a missile. Clapper estimated that “it would probably take Iran longer than a year to produce a nuclear weapon.”

Whether or not we’d even know if Iran decided to build a nuke is not clear. In 1968, Iran signed the Nuclear Non-Proliferation Treaty, which allows international inspectors from the International Atomic Energy Agency to confirm whether it is abiding by its commitment not to produce weapons. IAEA monitors at least some of Iran’s facilities, and would “almost certainly” detect attempts to produce weapons grade uranium in them, according to the Congressional Research Service.

But, CRS adds, “Tehran would probably use covert facilities for this purpose.”

So why is tension between the UN and Iran mounting? Under its treaty obligations, Iran must disclose all of its nuclear facilities to the IAEA, and allow inspectors to ensure that technology is not being used for bombs.

Iran has declared 16 nuclear facilities and nine sites where nuclear material is used. (This map locates and details some, and here’s a list of its nuclear-related sites.)

But the IAEA has long been frustrated (to put it mildly) by Iran’s lack of cooperation.

The current showdown began in August 2002, when an Iranian exile group held a press conference disclosing “that Iran had built nuclear-related facilities at Natanz and Arak that it had not revealed to the IAEA” according to the Congressional Research Service. At least some of this information proved to be accurate, and later inspections led IAEA to reveal “a variety of clandestine nuclear-related activities, some of which violated” Iran’s non-proliferation treaty obligations.

Presented with evidence that Iran may not be restricting its nuclear program to peaceful activities, the UN Security Council demanded that Iran cease work on uranium enrichment (and on a separate, as-of-yet-completed heavy-water reactor, which could ultimately produce plutonium, another nuclear weapon material). Iran has rejected these demands.

Moreover, Iran has blocked inspectors from examining Parchin, a military base where Western intelligence and satellite imagery have led experts to believe that Tehran could be testing nuclear bomb triggers, another key weapon technology.

Iran’s refusal to allow access means the agency is unable to “conclude that all nuclear material in Iran is in peaceful activities.”(This is discussed in IAEA reports filed in Feb. 2010, Nov. 2011, Aug. 2012, and in its most recent Feb. 2013 report.)

So far, however, the IAEA has “not found a smoking gun” implicating Iran in nuclear weapons production.

So will this latest round of negotiations end with a diplomatic breakthrough? French deputy foreign ministry spokesman Vincent Floreani said the Security Council was preparing to offer Iran "significant new elements." But based on the track record, an accord is not likely.

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