Iran's nuclear program, which could have the capacity to produce weapons-grade nuclear material sooner rather than later, remains a principal focus of international attention, despite a vast international policy crisis vis-a-vis the Middle East, due to the developments engendered by the so-called Arab Spring. The harshest sanctions regime applied in modern times is in place against Iran, even as other covert efforts, including a cyber-war intended to sabotage Iran's research, have been carried out, presumably by Israel and the United States. As a result of this global pressure, Iran has come back to the negotiating table to see if it can strike a deal that will alleviate some of the pressure.

Nonetheless, hawks in both Israel and the United States still maintain that bombing Iran's nuclear facilities is the only way to slow down, if not stop its nuclear progress. Yet the potential repercussions of such an escalatory step have not been sufficiently discussed in the media of either country. Rather, the debate has so far focused on the possible blockade by international forces of the Straits of Hormuz which, it is anticipated, would lead to a massive increase in oil prices. That in turn could be expected to severely affect the already recession-hit economies of Europe and the United States, not to speak of those poorer countries of the developing world that are dependent on Middle Eastern oil.

However, if Israel bombs Iran's nuclear facilities - a step that is bound to involve the United States, either actively or indirectly - Iran is unlikely to retaliate in an all-out confrontational style: by launching missiles against Israel, trying to sink U.S. ships in the Persian Gulf or even imposing its own closure of Hormuz. Instead Iran is far more likely to mobilize on the basis of the much wider support it can muster in the Muslim world, which is already seething with anti-American and anti-Israeli feelings.

The Islamic Republic's primary support would come from the small but politically active and well-financed Shia minorities that can be found in almost all the states stretching from Lebanon to India. In many countries like Pakistan or Afghanistan, the Shia communities constitute up to 15 percent of the population. In the Gulf state of Bahrain, and of course in Iraq, Shia constitute a majority.

Since the Iranian revolution, in 1979, Tehran has seen itself as both spokesman and protector of the global Shia population, even though many Shia may resent this fact. In this self-delineated role, it has funded local Shia organizations, provided educational scholarships to Shia students to study in Iran, trained and armed local Shia militias in such places as Lebanon, Afghanistan and Pakistan, and provided military training and education to young Shias in their countries of origin.

In the Arab states of the Gulf, for example, these Shia minorities are often at odds with their own regimes because of the lack of protection or respect they receive, or the prejudice that is inherent to many Arab Sunni fundamentalist regimes. In countries that border Iran, such as Iraq, Pakistan and Afghanistan, all of which are subject to a powerful U.S. military or political presence, Iran, to protect itself against possible American incursions or sabotage, has trained local militants to attack U.S. targets in their respective countries in the event of any attack on Iran. This program had its origins during the second term of the Bush administration, when Vice President Dick Cheney spoke openly about attacking Iran. Iran organized and planned for retaliatory attacks against U.S. targets everywhere that it was in a position to arm and fund clandestine groups.

Thus, the Shia protest in the Muslim world would likely be organized and widespread, and would target Americans and Israelis, and include major acts of terrorism and extreme violence.

At the same time, anti-Americanism is reaching dangerous levels in predominantly Sunni countries such as Pakistan and Afghanistan. Both countries have extremist Sunni groups that engage in terrorism, as well as conservative Islamic parties that participate in electoral politics. Any attack on Iran could see a merging of all these Sunni elements as well as of the broader Sunni population, and one could expect widespread anger in the streets.

Such widespread and angry protests could make it almost impossible for Americans or Israelis to travel, work or do business across the Arab world and the Indian subcontinent. Such protests would almost invariably wipe out the gains and aspirations of the democratic movements within the Arab Spring countries, and lead to a reinforcing of Islamic fundamentalist parties, which could be expected to jump on the anti-American bandwagon. Widespread Sunni protests would invariably make the U.S. and NATO withdrawal from Afghanistan planned for 2014 much more difficult and possibly lead to the strengthening of the Taliban. It also could lead to a possible new intifada among the Palestinians, who in any case see little hope of an agreement with Israel on a two-state solution.

Thus any attack on Iran can be expected to unleash a violent reaction throughout the Muslim world, both in the more organized Shia minority camp where Iran has influence and in the majority Sunni countries where Iran may not have influence but anti-Americanism certainly does. The risk will be greater for Israel than for anyone else - a state already isolated and besieged by hostile states. With its conflict with the Palestinians unresolved, it will find itself even more isolated and under threat. The United States will find itself besieged in many parts of the Muslim world, making normal diplomacy unworkable and the effort to enlist Muslim states to support the U.S. war against Al-Qaida more difficult.

Israel needs to carefully consider the consequences of any military action against Iran.

Ahmed Rashid, a Pakistani journalist and writer, is the author of five books, including the best-selling "Taliban" and "Descent into Chaos," and the newly published "Pakistan on the Brink: The Future of America, Pakistan and Afghanistan" (Viking ).