Analysis: How would Iran respond to an Israeli attack?
Iran has made it clear that if it is attacked either by Israel or the United States it will respond in kind. But just what could Iran do to strike back?
What would be the consequences, both in the region and inside Iran itself?
Indeed, could the potential consequences of an Israeli strike be so serious as to make military action the least preferable option in terms of constraining Iran's nuclear programme?
"Iran's ability to strike back directly against Israel is limited," says Mark Fitzpatrick, director of the Non-Proliferation and Disarmament Programme at the London-based International Institute for Strategic Studies (IISS).
"Its antiquated air force is totally outclassed by the Israelis and it has only a limited number of ballistic missiles that could reach Israel."
Mr Fitzpatrick says Iran's missile arsenal includes "a modified version of the Shahab-3, the Ghadr-1, which has a range of 1,600km (995 miles), but Iran only has about six transporter-erector launchers for the missile".
"Iran's new solid-fuelled missile, the Sajjil-2, can also reach Israel, but it is not yet fully operational," he adds.
But, Mr Fitzpatrick argues that "both of these missiles are too inaccurate to have any effect against military targets when armed with conventional weapons".
"Nor are they a very effective way to deliver chemical or biological weapons, and Iran does not have nuclear weapons."
In summary, he believes that "an Iranian missile strike would be only a symbolic gesture".
Mr Fitzpatrick believes Iran is more likely to respond against Israel "asymmetrically, and through proxies". Its ally, the Shia Islamist group Hezbollah, has more than 10,000 rocket launchers in southern Lebanon, many of them supplied by Iran.
"These are mostly 25km-range (16-mile) Katyushas, but also Fahr-3 (45km; 28 miles), Fajr-5 (75km; 47 miles), Zelzal-2 (200km; 124 miles) and potentially Fateh-110 (200km) plus about 10 Scud-D missiles that can pack a 750kg (1,653lb) payload and hit all of Israel."
He says that the Palestinian Islamist movement Hamas, which controls the Gaza Strip, could also attack Israel with shorter-range rockets.
The great danger here is of a more extensive conflict breaking out either between Israel and Hezbollah, or Israel and Hamas.
With so much instability in the Middle East - not least because of the Syria crisis - there is a very real risk of an Israeli strike sparking a much broader regional conflagration.
Naval action in the Gulf
The Iranian Navy, and especially the naval arm of its Islamic Revolution Guards Corps (IRGC), are well-equipped with small, fast craft capable of laying mines or swarming attacks against larger vessels.
Iran also deploys capable land-based anti-shipping missiles.
These could all be used to close off the vital oil artery - the Strait of Hormuz.
The US Navy is confident that it could re-open the Strait. But this risks an extended naval conflict between the US and Iran, and in the short term, there could be a significant impact upon oil prices.
Daniel Byman, a counter-terrorism expert at the Brookings Institution in Washington, says there is also "considerable concern that Iran and groups like the Lebanese Hezbollah might engage in terror attacks in the wake of an Israeli air strike".
"Iran has at times used such attacks to strike out at enemies, particularly those it cannot hit by other means," he adds.
There is already, he points out, a kind of clandestine war under way.
"Israel and Iran are already striking at each other (Israel with more success and doing so in a way that is more targeted)," Mr Byman explains, referring to the assassination of Iranian nuclear scientists.
"I'm not sure Israel would increase attacks in the wake of a strike," he notes, "but Iran would."
Mr Byman is uncertain about how effective such Iranian operations might be.
"Iran's reported attempted attacks in India and Thailand show it remains determined to strike at Israel, presumably in retaliation for Israeli killings of Hezbollah figures like Imad Mughniyeh and the suspected attacks on Iranian nuclear scientists."
"However, these recent attacks were not well executed, suggesting that Iran's services' professionalism is uneven," he argues.
Overall, experts believe that the Iranian government is going to have to calibrate its response to any attack carefully.
Karim Sadjadpour, an Iran expert at the Carnegie Endowment for International Peace, told me: "If they respond too little, they could lose face, and if they respond too much, they could lose their heads."
"Iran will want to respond enough to inflame the regional security environment and negatively impact the global economy - in order to bring down international condemnation of the US or Israel - but stop short of doing anything that could invite massive reprisals from the United States."
"Frankly," Mr Sadjadpour says, "I'm not sure how they do that. If Iran tries to destabilise world energy supplies - whether launching missiles into Saudi Arabia's oil-rich eastern province or attempting to close the Strait of Hormuz - the US isn't going to stand aside idly."
In the wake of any attack on its facilities, Iran might well, of course, go to the UN to seek some kind of diplomatic redress. This highlights a crucial set of legal questions relating to any military operation.
For all the uncertainties as to whether Israel would attack Iran and indeed how Iran might respond, one thing is clear - in terms of international law, such a strike would be illegal.
Professor Mary Ellen O'Connell, professor of international law at the University of Notre Dame, says for it to be considered legal, "the UN Security Council would need to authorise such a strike, because Iran has not launched an armed attack on either Israel or the United States".
"The UN Charter," she says, "makes clear that the use of force is generally prohibited unless a state is acting in self-defence to an armed attack occurring, or has Security Council authorisation."
Israel, of course, would probably claim to be acting in some pre-emptive sense to forestall a future nuclear attack from Iran (though nobody yet believes Iran has a nuclear bomb). But Professor O'Connell says that an Israeli strike would still not be legitimate.
"There is a lively debate among international lawyers as to the point at which a state may respond to an armed attack: must it be under way or merely imminent?"
"There is virtually no support among experts for attacking to 'pre-empt' a hypothetical future attack."
But surely countries do what they believe they have to do when vital interests are seen to be at stake?
For example, Nato attacked Serbia and Serbian forces in Kosovo, and the US and its allies invaded Iraq - both examples lacked UN Security Council approval.
Professor O'Connell says that in both cases, the illegal use of force came with costly penalties.
"Compare those two conflicts," she notes, "to the lawful use of force to liberate Kuwait after Iraq's invasion. The United States came out of that conflict with a financial and moral gain."
Many will also raise the question of the potential casualties that any Israeli strike might cause, especially since the operation would not be sanctioned by international law.
Without knowing the targets to be hit, the timing of any strikes, and the likelihood of them being hit again, it is hard to determine potential casualty figures.
Experts say that the functioning nuclear reactor at Bushehr is unlikely to be a target due to the fact that it has nothing to do with a potential military programme and radiation leakage could cause widespread civilian casualties. But, of course, aircraft can be downed and bombs and other air-launched weapons can go astray.
There are, in addition, another set of Iranian reactions to any strike that matter.
How would Iranians themselves respond to any attack? What would be the impact upon Iran's nuclear programme? And what would be the implications for the Islamic regime in Iran itself?
For now, it seems unclear that Iran has actually yet taken any decision to press ahead with a nuclear weapons programme.
But Trita Parsi, author of the recently published, A Single Roll of the Dice - Obama's Diplomacy With Iran, says that if Israel attacks, Iran's position will change considerably.
"I have not come across any observer who does not believe that the Iranian government's determination and desire for a nuclear deterrent would increase several-fold if Iran is attacked."
The US assessment, he says, is that in the wake of an Israeli attack "the Iranians will push their program further underground, exit (or threaten to exit) the Non-Proliferation Treaty, kick out the International Atomic Energy Agency (IAEA) inspectors and dash for a bomb".
"As some senior American military officials have said, bombing Iran is the fastest way to ensure an Iranian bomb," he adds.
Mr Parsi, who is president of the National Iranian American Council, also says that an Israeli attack would have political implications inside Iran too.
"The Iranian regime is deeply unpopular and the wounds from their massive human rights abuses since the 2009 election are still open and bleeding."
The regime, he adds, "has thus far failed to overcome this division with the people".
"However, an attack on Iran, particularly if the bombing campaign also results in high civilian casualties, will likely unite warring factions in Iran against the external aggressor."
"This is what happened in 1980 with Saddam Hussein's invasion of Iran."
"The attack helped consolidate Ayatollah Khomeini's grip on power, fuel nationalism and revolutionary zeal, and suspend the internal power struggles. The Iranian regime didn't survive in spite of Saddam's attack, but because of it."
That should be a sobering thought for Western and Israeli policy-makers, who from time to time flirt with the idea of regime change in Iran.
It all suggests a stark conclusion - even a militarily successful attack from Israel's point of view will only delay Iran's nuclear programme for a few years.
It might indeed confirm Iran in its desire to obtain a nuclear weapon. It might rally the Iranian population around the regime. And the regional consequences of any air strikes could be considerable; at worst precipitating conflict in the Gulf and on Israel's own borders.
No wonder, then, that the Obama administration seems to be trying to dissuade Israel from any attack - at least for now.
Many experts believe that there is still mileage in allowing sanctions to take their course but also - even now - in reaching out diplomatically to Tehran.
"Diplomacy has certainly not been exhausted," Trita Parsi told me. "The diplomatic efforts in the past few years have been few and short-lived," he notes.
"Political space for the type of sustained talks that are needed to generate a breakthrough has not existed in Washington or in Tehran. Rather than real negotiations, we have seen an exchange of ultimatums."
Karim Sadjadpour also thinks it may be worth another diplomatic push. But he feels the potential results will inevitably be limited.
"How do you reach a rapprochement with a regime that needs you as an adversary for its own ideological legitimacy?" he asks.
"Realistically," he concludes, "I think dialogue with Tehran can at best contain our differences with Iran, but it won't resolve them."