The US and its allies are planning to ratchet up severe sanctions against Iran, in light of the decision of the leadership of the Islamic Republic to rebuff Western diplomatic offers and to go ahead with domestic enrichment of its low-enriched uranium to the 20 per cent level. This new stage of enrichment will put Iran within range of making the last sprint to 90 per cent enrichment to fuel a nuclear weapon. Severe sanctions are an important step but they should have been undertaken more than a year ago. And it is now necessary to understand more than ever the full implications for the West, should there not be enough time for sanctions to kick in and Iran crosses the nuclear threshold in the interim. Privately, in many Western capitals there is the dangerous belief that in the worst case, a nuclear Iran can be deterred, just like the Soviet Union was deterred during the Cold War.
 
If this is Plan B, it won't work. Should the West make this error and acquiesce to Iranian nuclear weapons, the U.S. and its allies will begin their deterrence relationship with a nuclear Iran with a huge handicap. Despite the fact that Western statesmen stated for years that nuclear weapons in the hands of Tehran were "unacceptable," Iran will have proved that it successfully defied repeated warnings about its program. What credibility will further warnings to Iran have at that time?

Moreover, Iran's primary threat to the West has been its direct support for terrorist organizations, like Hezbollah, as well as for Sunni terror groups, all with worldwide reach. In the last few years, under Ahmadinejad, the Iranians have made serious inroads in Latin America, especially in Venezuela, establishing new networks for future Hezbollah operations. A nuclear Iran can tell its operatives worldwide that they can attack with virtual impunity, protected by Iran's new nuclear umbrella from any retaliation. It was an offer that the Taliban, who hosted al-Qaeda in 2001, could not make in Afghanistan, but which every radical Islamic terrorist group will increasingly seek once Tehran puts it out.

Will Iran transfer its nuclear weapons to terrorist groups? In 1983, when Iran ordered the attack on the U.S. Marine barracks in Beirut, its operatives created the largest non-nuclear explosion that had ever been detonated on the face of the Earth. Tehran was determined to evict the U.S. from Lebanon to consolidate its control, and was only limited by its technological capabilities at the time. Today, Iran is showing no reluctance to transfer to its terrorist arm, Hezbollah, the latest, state-of-the art, conventional weaponry that was never provided in the past to terror groups: from anti-ship missiles to shoulder-fired anti-aircraft systems, and even rockets with ranges of over a hundred miles. In the Iranian security establishment the barriers that might have once existed between the weaponry reserved for Iranian military units and the weaponry supplied to Hezbollah have been coming down. Given al-Qaeda's interest in nuclear weapons, it would be a cardinal error to assume that Iranian-sponsored groups will not take a similar interest and seek Iranian nuclear assistance, perhaps limiting themselves initially to a "dirty bomb," which was once employed, albeit unsuccessfully, by a Chechen group in 1995.

Then there is the question of Israel. Iran has ambitions across the Middle East, but its leadership is obsessed by Israel's very existence. Ayatollah Ali Khamenei once told the former Spanish prime minister, Jose Maria Aznar, in a private audience in 2001 that it was Iran's goal "to set Israel on fire."  This was not rhetoric for public consumption. It was stated years before President Mahmoud Ahmadinejad made his declarations to the same effect. It was repeated in other ways by the heads of the Iranian security establishment, including General Mohammad Ali Jafari, the commander of the Revolutionary Guards, who spoke in 2008 about "the destruction of the cancerous microbe Israel." This drumbeat continues. Yesterday, Ahmadinejad said Israel was on the verge of "annihilation". To say, as some analysts suggest, that Iran is developing nuclear weapons for deterrence alone, as it repeatedly issues blatant existential threats to eradicate Israel, is plainly wrong and irresponsible. And Israel must do everything in its power to prepare itself for the threat it will face.

Iran's crossing the nuclear threshold and acquiring nuclear weapons will have global implications that have unfortunately not been fully recognized. This will not be another case like that of Pakistan or North Korea. The Islamic Republic is truly a revolutionary regime that wants to re-shape not only the Middle East but world politics as a whole. In this spirit, General Jafari told his officers in 2008: "Our Imam did not limit the movement of the Islamic Revolution to this country, but drew greater horizons."

True, Iran wants to dominate the oil-rich Persian Gulf and control the energy sources of the industrial world. Its navy conducts exercises on both sides of the 34-mile-wide Strait of Hormuz, through which some 40 percent of the world's oil moves by tanker. It has exploited Sunni-Shiite frictions throughout the area from Iraq through Kuwait, Bahrain and Saudi Arabia, using Hezbollah branches backed by the Revolutionary Guards, as it ultimately seeks to topple pro-Western governments.
Some of these governments will huddle under a Western umbrella for protection from a nuclear Iran. But mostly, the nuclearization of Iran will set off a chain reaction across the Middle East, as Egypt, Saudi Arabia, Turkey and others seek their own nuclear weapons. For these reasons a nuclear Iran must be prevented at all costs.