We are now moving into the endgame of Iran’s decade-long drive to acquire the hardware and technology to build a nuclear bomb. What happens next could determine whether Iran becomes a nuclear-armed state, whether the region is plunged into another war, or whether Iran and the Arab world embark on a nuclear arms race.

Yesterday’s announcement showed that President Ahmadinejad has once again calculated that attack is the best form of defence. After being censured by the International Atomic Energy Agency (IAEA) last week, which referred Tehran to the UN Security Council, the Iranians have decided to call the bluff of the international community.

They believe that the world is unwilling or unable to take serious steps to prevent it from building its own uranium enrichment industry. Enriched uranium can be used as nuclear fuel or, in its highly enriched form, provide the fissile material to build an atomic warhead.

In the past, meaningful action by the UN Security Council in the form of economic sanctions has been blocked by Russia and China, which have major commercial ties with Iran. The Iranians have also been working hard to bolster their position in the international community. Although regarded as a pariah in the West — particularly after the contested presidential election results this summer — Mr Ahmadinejad is still welcome in many capitals around the world, most recently Brasilia and Caracas.

The Iranian strategy is clear: defy the West, woo Moscow and Beijing and build up support in the developing world.

Iran has calculated that the Obama Administration, which offered this year to end three decades of hostility, is distracted by the domestic problems and the war in Afghanistan. Europe still fails to speak with one voice on this matter. As for the rest of the world, an increasing number of states believe that Iran will now build the bomb and is prepared to live with this fact.

However, it would be a huge miscalculation to believe that the problems will stop there. Israel regards the issue as an existential threat and has warned that it is prepared to launch a pre-emptive strike to destroy Iran’s nuclear facilities — even if this means starting a new war in the Middle East. The Arab states are caught in the middle. Many have decided that their best option is to start their own nuclear programmes, as Egypt and the Gulf states are already doing.

The crisis is likely to feed into the escalating tensions in the region between Sunni and Shia Muslims. Already at odds in Lebanon, Yemen, Iraq and the Gulf states, further hostilities could break out with Iran, the main Shia power in the region, as it supports its brethren against the Arab states.

The only move that could stop an escalation would be concerted action by the UN Security Council. Iran’s economy remains vulnerable to outside pressure; this is where American, British and other Western diplomats will hope to squeeze Tehran into backing down.

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