IN THE West, public opinion is hardening against the prospect of a nuclear-armed Islamic republic. Inside Iran, the public has been galvanised by its leaders into mobilising in support of the country's nuclear program.
Iran's President Mahmoud Ahmadinejad, a former member of the fanatical Revolutionary Guards, set alarm bells ringing by threatening to "wipe Israel off the map".
Diplomatic moves are at a standstill because of reluctance from Russia and China to impose sanctions against Iran, which has important support from developing countries where nuclear power is seen as a legitimate right.
In the West, arms control experts are convinced Iran wants to pursue uranium enrichment at its underground facility at Natanz with the intention of keeping open the option of building a bomb.
The difference between enriched uranium for a nuclear power plant and for a weapon lies in the level of enrichment. Fuel for a civilian reactor requires 2-3 per cent of uranium-235, while a nuclear bomb needs 90 per cent or more, a range known as highly enriched uranium.
The Iranians will have mastered the technology that can allow its centrifuges to enrich uranium without exploding or breaking down in a matter of months, according to Western experts. When that happens, Israel's arch foe will have a powerful tool with which to threaten its neighbours.
Estimates vary as to how long it would take Iran to reach the break-out capability. The generally cautious director-general of the International Atomic Energy Agency (IAEA), Mohamed ElBaradei, believes it could take up to two years for Natanz to be up and running.
At that point, he says, an Iranian nuclear bomb could be "a few months away".
American estimates range from five to 10 years for weapons-grade fuel to be successfully manufactured.
According to a study by the International Institute for Strategic Studies, with 1000 working centrifuges at Natanz, it would take just over two years to produce enough highly enriched uranium for a bomb - without the IAEA safeguards which are currently in place.
With 3000 centrifuges - the number Iran has told the Europeans it wants to install at Natanz - it would take 271 days to produce the same amount of weapons-grade fuel.
According to one expert, such a fuel cycle would be a clear indication that the Iranians are bent on building a bomb.
One way to make a nuclear weapon is to begin with uranium. Uranium hexafluoride gas is fed into 1.5m tall centrifuges, where the uranium enrichment takes place. This process increases the percentage of uranium-235 to the levels needed to be used as fuel in a civilian reactor, or a weapon, by separating the uranium isotopes in the rapidly spinning rotor tubes.
But there are well-known problems with gas centrifuges. If they do not operate in a vacuum, rust and corrosion sets in. The spinning at enormous speeds can cause uncontrollable vibrations that can send shrapnel flying and cause explosions. The Iranians are still trying to figure out how they lost one-third of their centrifuges when they agreed to halt uranium enrichment in November 2003 under an agreement with the European Union. That agreement was shattered last January when Iran reopened Natanz, where it tested an array of 20 centrifuges in vacuum conditions.
Making a nuclear weapon involving plutonium has a clear advantage because it needs much smaller quantities - four kilos - than the 25kg of enriched uranium required to produce a bomb. Plutonium does not exist in a natural state, and is the product of reprocessed spent reactor fuel.
The extraction of plutonium is a serious engineering challenge as spent fuel is highly radioactive and toxic. It's a very dangerous process. The main worry for the West is that Iran has dabbled in all aspects of the nuclear fuel cycle, on both the enriched uranium route and the plutonium route.
It has a uranium mine, it has a conversion facility just outside the city of Isfahan, which was reopened last year in violation of its agreement with the EU, and it has the Natanz enrichment plant.
Although work has been suspended, at Arak, 240km south of Tehran, Iran is in the early stages of constructing a heavy water plant to supply a research reactor that could eventually produce enough weapons-grade plutonium for one or two weapons a year. The Iranians also have an experimental reactor at the Tehran Nuclear Research Centre, where it has admitted to plutonium separation experiments.
Iran does not have a confirmed reprocessing facility, but French intelligence has reported Iran tried to buy reprocessing equipment from French companies in 2000 and 2002.
Although nuclear experts say the international community has been distracted by the crisis triggered over Iran's uranium enrichment program, the plutonium experiments have the potential for creating a far more worrying situation.
"With uranium, it's much easier to put in safeguards to monitor the atmosphere and instruments," said Paul Ingram, a senior analyst with the British American Security Information Council, which specialises in nuclear issues.
Nuclear reprocessing is more difficult for inspectors to verify, in terms of possible diversion for military purposes. And reprocessing can take place in a very small area.
"It could be done in a plant the size of a house, in the middle of a mountain," Ingram said.
“If the Iranians succeed in producing a heavy-water plant plus a reactor at Arak, then we are in a very difficult situation."
The Russians are helping Iran build a "safe" light-water reactor at Bushehr in the south of the country. Under an agreement with the Russians, the fuel rods for the reactor, which has not yet come on stream, are to come from Russia and sent back there for reprocessing to avoid any possible diversion.
The main nuclear powers took the reprocessing route to build their modern arsenal. The US experimented with the fuel cycle of both enriched uranium and plutonium - the bomb that flattened Hiroshima in August 1945 was a uranium bomb, while the bomb that blasted Nagasaki three days later was plutonium.
Pakistan took the enrichment route, most likely because the father of the Muslim world's atom bomb, A.Q. Khan, worked in the 1970s for a Dutch uranium enrichment plant, Urenco, which supplied European reactors. He used a centrifuge design stolen from Urenco to build facilities in Pakistan for weapons-grade uranium.
The Iranians were following both routes from the beginning. They bought their first nuclear reactor from the Americans, during the rule of the Shah. In the 1980s Iran bought a blueprint for a centrifuge from the A.Q. Khan network that operated like a nuclear supermarket.
UN inspectors with the IAEA are still trying to unravel the history of Iran's nuclear know- how and have not proved without a doubt that the Iranians are working on a bomb.
