American and Israeli military planners have been examining options for an attack on Iran for almost three decades. There is no shortage of possible targets: Iran has dozens of nuclear-related sites that are known to western officials.

Yet military experts in Washington and Tel Aviv acknowledge that a surprise airstrike would be likely to succeed only in delaying Iran’s development of nuclear weapons. It would also present daunting logistical and political challenges with no guarantee that even a sustained assault on known facilities would eradicate Tehran’s nuclear threat.

With President Barack Obama committed to diplomatic pressure, the most likely military scenarios involve Israeli airstrikes that would require mid-air refuelling and long flights through potentially hostile Arab air space. “Anyone who meets regularly with senior Israeli officials knows that Israel is considering military options ... with an understanding that they pose serious problems and risks,” said Anthony Cordesman, a former Pentagon planner.

The three likeliest targets for an Israeli attack are reactors at Bushehr and Arak and a centrifuge production facility at Natanz. All are 1,000 miles or more from Israel, at the outer operating margins of Israeli air force bombers.

The Bushehr light water reactor is being built and fuelled by Russia and is not yet operational. Any attack on it would be certain to infuriate Moscow and might provoke the Russians into supplying Iran with more advanced anti-aircraft defences.

The heavy water reactor at Arak has been at least partially sheltered from air attack and is not expected to be completed for several years.

The Natanz facilities have also been sheltered underground and are defended by short-range Russian TOR-M surfaceto-air missiles.

The Israeli air force is equipped with US-supplied GBU-28 earth-penetrating bombs designed to destroy underground targets. Israel may also have developed its own variant of a nuclear-tipped bunker-busting bomb.

Yet the real problem for military planners is that no outside agency has a clear idea of where else Iran may have hidden its weapons-related technologies, notably the long-range missiles that might one day deliver nuclear warheads.

“It is doubtful that even the US knows all the potential targets,” said Cordesman. “They may now be in too many places for an Israeli strike to destroy Iran’s capabilities.”

US experts believe that while Israel unquestionably has the military capability — and may have the political will — to mount a long-range attack, it could not sustain the kind of long-term barrage that Washington launched against Baghdad in the early phases of two Gulf wars.

The diplomatic uproar that would be certain to follow any Israeli attack might limit Tel Aviv to a one-off operation that it could never hope to repeat. “That would not be on the scale required to do more than delay parts of the Iranian programme,” said Cordesman.

Only if America joined in would Iran have reason to worry. There is no immediate likelihood of a US military strike; but there are still some in Tel Aviv who believe that an Israeli raid might force Obama’s hand and persuade the Pentagon to join the attack.

Times Recommends

• Times Charity Appeal: SolarAid
• Is it Black Monday all over again for Dubai?
• Behind the scenes at the biggest deal