Iran's nuclear gambit - the basics

Iran's President Mahmoud Ahmadinejad has written a letter to President Bush in a bid to ease global tensions, Iranian officials said Monday. This is the first such direct, high-level public communication between the two countries since Islamic revolutionaries took over the US Embassy in 1979.

The letter, which mentions Iran's contentious nuclear program, comes during a week when the US is trying to marshal key United Nations Security Council foreign ministers for a resolution that would compel Iran to suspend uranium enrichment - with the implied threat of sanctions and military enforcement. But Tehran says its program is legal and will continue.

Mr. Ahmadinejad's letter "spoke of the current tense situation in the world and suggested ways of solving problems and of easing tensions," Iranian government spokesman Gholamhossein Elham said Monday.

US Director of National Intelligence John Negroponte, who had not yet seen the letter being passed to Washington through the Swiss Embassy in Tehran, suggested that the "timing of the dispatch of that letter is connected with trying in some manner to influence the debate before the Security Council."

Taking a strident tone Sunday, Ahmadinejad warned of UN action: "They should know that the Iranians will dash their illegitimate resolution against the wall."

As this high-stakes diplomacy gets under way, the Monitor's Scott Peterson explores some basic questions about Iran's nuclear program:

Somewhere between two and 10 years. But the answer to that question depends upon whom you ask, and whether you accept that Iran will stick to a peaceful atomic energy program - as Iranian officials declare. Three years of UN inspections have not produced a definitive answer.

Some US politicians allege that the Islamic Republic is secretly trying to acquire nuclear weapons, and that mili- tary force can be used to stop any such work. But the International Atomic Energy Agency (IAEA), the UN nuclear watch- dog, has found no evidence of such a decision by Iran.

Mr. Negroponte, testified to Congress in February that Iran "will likely have the capability" to produce a nuclear weapon within 10 years.

In late March, the Institute for Science and International Security (ISIS), which closely tracks Iran's nuclear issues, calculated a "worst case" estimate of "at least three years" before Iran would have enough fissile material to make a bomb. The ISIS added that, "it could take Iran much longer" because of technical difficulties.

Some of the shortest estimates, of less than two years, come from Israel, which maintains its own unofficial nuclear arsenal. Many analysts argue that Iran has made no decision to build a weapon, but instead desires a "threshold" capability to make one within months.

Though American forces in the Middle East and Israel are within the 1,000-mile range of Iran's Shahab-3 missiles (Iran claimed upgrades to 1,240 miles in 2004), experts say that building a nuclear device small and light enough to be carried as a payload for such a distance is extremely tricky business.

US officials reportedly briefed the IAEA last July on designs it claims were found on a laptop - stolen by an Iranian, and acquired by US intelligence - which it said showed warhead designs modified to accommodate a compact nuclear warhead. US experts question the significance of the allegations, first reported by The New York Times last November. Iran rejects the charge as "a worthless attempt to fabricate a scenario," but the IAEA on April 28 reported that it is one issue Iran "has yet to address."

Further reports, denied by Tehran, emerged from diplomats at the IAEA headquarters in Vienna in early March, suggesting that Iran has covert plans to arm the Shahab-3 with a nuclear warhead. News reports from Germany last December suggest that Iran may have purchased 18 BM-25 disassembled missiles, which have a range of 1,550 miles, from North Korea.

Rumors and news reports hint at a longer range missile on the drawing board. Iranian military officials claimed last month to have successfully test-fired a short-range radar-avoiding antiaircraft missile and a new high-speed torpedo.

The success of Iran's nuclear program hinges upon its use of centrifuges. They are machines that literally "spin" uranium into an enriched form, to be used either for nuclear fuel to produce power, or, at a much higher level, to make atomic bombs.

As US-led diplomatic pressure grew to report Iran to the UN Security Council, last January Iran removed IAEA seals in the presence of international nuclear inspectors and resumed work.

Iran announced last week that it had enriched uranium to 4.8 percent U-235. That is the top end of the scale needed to power a nuclear reactor, but far from the 80 to 90 percent required for a weapon. Gholamreza Aghazadeh, the head of Iran's Atomic Energy Organization, said that "enrichment above 5 percent is not on Iran's agenda."

Iranian scientists are using a test "cascade" of 164 centrifuges, are building two more similar sized cascades, and plan to install 3,000 centrifuges by the end of this year - a number that could produce enough nuclear material in a year, by one count, for a single bomb.

Iran has told the IAEA of plans for 54,000 centrifuges at the underground site at Natanz, though the ISIS estimates that Iran has quality components for 1,700 to 2,700 centrifuge assemblies.

As a signatory to the nuclear Non- Proliferation Treaty (NPT), Iran is obligated to declare all its nuclear facilities and use of nuclear material, and to keep them under IAEA safeguard. Iran is also permitted, under the NPT, to pursue nuclear energy programs, and uranium enrichment for that purpose. The same treaty also obligates signatories with nuclear weapons, including the US, to move toward total disarmament.

Iran has stated repeatedly that it has no intention of going beyond nuclear energy, but in 2002 an Iranian opposition group living in exile - reportedly tipped off by Israeli intelligence - revealed the undeclared enrichment site at Natanz and work on a heavy-water research reactor at Arak.

Iran was found to have kept those and other key aspects of its nuclear program secret for nearly two decades. It is also known to have had dealings with the proliferation network of Pakistani nuclear scientist A.Q. Khan, who sold nuclear blueprints to Libya and other clients around the world.

To increase confidence in its peaceful intentions, and show goodwill, Iran voluntarily suspended enrichment. Until Feb. 5, Iran largely acted as though it had ratified the Additional Protocol of the NPT, which provides for intrusive inspections.

But while Iran has helped resolve many issues, cooperation has not been complete. The IAEA report to the Security Council on April 28 notes that "gaps remain in the Agency's knowledge" that "continue to be a matter of concern," and will require "transparency that goes beyond [the] Additional Protocol" to clear up.

Iran adheres to its "right" under the NPT to enrich uranium for peaceful purposes, but has downgraded its cooperation with the IAEA to "minimal" safeguard obligations. A letter from Iranian parliamentarians to UN Secretary General Kofi Annan Sunday called for a "peaceful" solution, and warned that increasing UN pressure would prompt Iran to "review" its NPT status. Withdrawal from the treaty would end UN inspections and all international oversight.

The US, Britain, and France are pushing this week for a resolution that impels Iran to stop uranium enrichment. Washington foresees sanctions on Iran, though Russia and China object. Both have extensive trade ties with Iran, and Moscow is building Iran's first nuclear power reactor, an $800 million project at Bushehr.

Mr. Annan last week called for direct US talks with Iran to find a solution, an option that has gained credence with some US analysts in the past year. Iran has hinted it could limit its nuclear ambitions in exchange for security guarantees.

Senior US officials say they prefer a diplomatic solution; for years, the US has negotiated with North Korea to contain its nuclear weapons program. But Russian and Chinese diplomats and many Western experts are skeptical about US intentions in Iran. President Bush refuses to rule out military action.

British Prime Minister Tony Blair said Sunday that any consideration of a nuclear attack against Iran would be "absolutely absurd."

But several reports in recent months suggest that American preparations to hit Iran's nuclear infrastructure - perhaps including the first-ever use of tactical nuclear weapons against hardened, underground targets - are already under way.

While military action could set back Iran's nuclear programs by several years, experts say they would also have several negative, long-term side effects. Iran would almost certainly withdraw from the NPT, and probably move secretly and with full determination to build nuclear weapons.

Iran could retaliate by slowing down oil through the Persian Gulf. Iran's Revolutionary Guard and other Iranian security forces have created networks in Iraq since the 2003 US invasion. Those could be encouraged to strike at US forces already grappling with a lethal insurgency.

Iran can also urge its Hizbullah ally in Lebanon to strike targets in northern Israel. Any attack would also prompt nationalist Iranians to rally around their leadership.

"Rather than living with an Iran that had the potential to produce nuclear weapons, the US action would almost certainly guarantee an overtly nuclear-armed Iran for decades to come or, alternatively, further instances of military action," warns a February analysis by the Britain-based Oxford Research Group.

The negative consequences "would be substantially greater" than the current conflict in Iraq, the report concludes, such that a military response "is a particularly dangerous option and should not be considered further."

• Matt Bradley contributed reporting to this piece.