<em>Illustration: John Shakespeare</em>

Illustration: John Shakespeare

For years, the world has been increasingly worried that Iran's progress towards a nuclear bomb would lead to war. Such a war could have unpredictable consequences, including consequences for Australia.

If Israel attacked Iran's nuclear facilities to halt its bomb building, it would very likely be supported by an Australian government, Liberal or Labor. And that might provoke retaliatory Iranian-backed terrorist attacks on Australians, for instance.

So now that there's an interim deal to halt Iran's bomb building, why isn't everyone happy?

The six major powers that struck the deal claim a historic breakthrough.

''For the first time in nearly a decade, we have halted the progress of the Iranian nuclear program and key parts of the program will be rolled back,'' says US President Barack Obama.

Or is it a ''historic mistake'', as Israel's Prime Minister, Benjamin Netanyahu, says? According to Israel, the Iranians have tricked the six powers and will keep working towards the bomb despite the deal.

On Sunday, Israel's Trade Minister, Naftali Bennett, went so far as to say: ''If, in five years, a nuclear suitcase explodes in New York or Madrid, it will be because of the agreement that was signed this morning.''

Israel isn't the only near neighbour of Iran's to worry, just the noisiest. Like Israel, Saudi Arabia is a key adversary of Iran's. The Saudis have not spoken officially but unofficially they also think the interim deal lets Iran off the hook.

Why is Iran negotiating at all? Global sanctions on Iran's economy have put a foot on the throat of the rising Middle East power.

Iran's new President, Hassan Rouhani, who replaced firebrand Mahmoud Ahmadinejad in June, made it his first priority to ease some of the pain for his people.

The six powers that negotiated the deal - the five permanent members of the United Nations Security Council plus Germany - believe the sanctions combined with the advent of Rouhani to create an unmissable chance to break Iran's progress towards a bomb.

But Israel and Saudi Arabia argue that the deal eases the pressure on Iran's throat; this gives it the oxygen and time to continue covertly towards bomb building, they say.

The US and its allies were hoodwinked so often, and so expertly, by another bomb-building nation, North Korea, that the doubters need to be taken seriously.

The six do not claim that the interim Iranian deal is enough. They have given themselves and Iran six months to reach a final and more comprehensive agreement.

So why do an interim deal at all? Why not keep the foot on the throat until Iran capitulates comprehensively?

The Obama administration argues that the world needs to quickly reward Rouhani and his chief negotiator, Mohammad Javad Zarif, and the moderates in Tehran.

The New York Times quoted an anonymous US official as saying: ''Zarif says he has, at most, six months to get a deal before the hardliners rise again. And we believe him.''

The central difference between the US-led six on the one hand and Israel and Saudi Arabia on the other? While Washington and its partners may believe the Iranian negotiator, Jerusalem and Riyadh do not believe a single syllable.

The main elements of the deal?

The US and its partners made two main concessions to Tehran. One is on uranium enrichment.

The UN Security Council had demanded that Iran freeze its enrichment altogether. This was a core stipulation.

The new deal allows it to continue but only up to 5 per cent enrichment. This concentration is enough to generate electricity, which Iran claims is its only aim, but not enough for a bomb. Iran has been enriching up to a level of 20 per cent, which only makes sense if it intends to develop a bomb.

Second is that Iran was allowed some very modest financial relief from the sanctions with a total value of about $US7 billion ($7.6 billion).

In return, Iran agreed to four key measures. One, to stop enriching uranium beyond 5 per cent. It also agreed to diluting all stockpiles to 5 per cent or less.

Two, Iran agreed to stop introducing new machines for enriching uranium, centrifuges, although it gets to keep all its existing ones.

Three, Iran agreed to halt construction of a new heavy water nuclear reactor that would have allowed it to make an alternative bomb fuel, plutonium.

Four, Iran agreed to allow better access to international inspectors from the International Atomic Energy Agency.

On balance, according to a respected independent American expert on nuclear proliferation, David Albright, ''the short-term deal accomplishes a great deal''.

The greatest risk to the agreement? The US Congress. It's unlikely to support the deal reached by the Obama administration, according to experts.

''This agreement makes a nuclear Iran more likely,'' said Senator Marco Rubio, touted as a Republican presidential candidate in 2016.

Some Republicans claimed the whole thing was confected to distract from problems with so-called Obamacare, the health insurance program. Key Democrats are also opposed. Senate opinion is more closely aligned with Netanyahu than Obama.

The deal ''makes it more likely that Democrats and Republicans will join together and pass additional sanctions when we return in December'', said Senator Chuck Schumer, a Democratic ally of Obama's.

That would destroy the deal. The most realistic prospect of avoiding war may yet be lost, even before a final deal can be negotiated.

Peter Hartcher is the international editor.

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