US strikes on Iran may have set the country’s nuclear programme back by several years, according to preliminary expert analysis.

Donald Trump’s claims that Iran’s nuclear sites had been “completely and totally obliterated” were likely to be an overstatement, serving and former US military officials said – but it is probable that all three facilities targeted suffered extensive damage.

Under best-case assessments, Iran’s capacity to enrich uranium has been severely degraded, if not destroyed. But the country’s existing stockpiles of uranium enriched to near weapons grade – enough to fuel 10 nuclear bombs – is thought to have survived.

Understanding the extent to which the US has damaged Iran’s nuclear programme is a vital in determining whether the strikes were a one-off or merely the opening salvo of a wider conflict.

America’s B-2 stealth bombers and cruise missiles struck Iran’s three most important nuclear sites: Fordow, Natanz and Isfahan. If the strikes succeeded in destroying centrifuge halls at the facilities, it would prevent Iran from further enriching its uranium stockpiles to a purity of 90 per cent – something it has not done so far, according to UN inspectors.

Satellite images of convoys leaving all three sites in recent days support Iran’s claims that it moved its 400-kg stockpile – much of it previously held at Isfahan – to a secret underground location shortly before the strikes.

But the damage inflicted elsewhere would still make it difficult to turn the uranium into a bomb.

Even if Iran had retained its fissile material, it would be “like having fuel without a car”, said Ronen Solomon, an Israeli intelligence analyst.

“They have the uranium – but they can’t do a lot with it, unless they have built something we don’t know about on a small scale.”

That is not beyond the realm of possibility. Iran succeeded in keeping its Fordow facility a secret for seven years before it was dramatically exposed, by Barack Obama, Gordon Brown and Nicolas Sarkozy – then the leaders of the US, UK and France – at a joint press conference in 2009, following a joint intelligence operation.

Fordow

Of the three sites attacked, Fordow was by far the most important.

The last-known site developed by the Iranians was deliberately designed to withstand aerial attack.

An “engineering marvel”, in the words of one Western official, its main centrifuge halls lie buried up to half a mile inside a mountain.

Not only does a layer of solid rock act as a natural shield impervious to most bombs, but additional artificial layers of reinforcement are also believed to have been added.

The GBU-57 Massive Ordnance Penetrator bunker-busting bomb – 12 of which the US dropped on Fordow – is capable of penetrating 60 metres of standard concrete before exploding.

But Iran is believed to have reinforced the centrifuge halls at Fordow with ultra-high performance concrete (UHPC), which can withstand six times the amount of pressure of normal concrete – up to 30,000lb per square inch. If Iran used the best quality UHPC, Fordow would have been significantly harder to destroy.

Given that the site is underground, it remains difficult to assess the scale of the damage yet, with both Iranian and US officials saying they are still conducting evaluations.

Natanz

Above-ground facilities at Natanz, Iran’s largest enrichment site, had already suffered extensive damaged by Israeli strikes, as shown by satellite imagery.

The destruction of the site’s electric substation may have knocked out power, potentially damaging centrifuges by causing them to spin out of control, according to the International Atomic Energy Agency, the UN’s nuclear watchdog.

Natanz also housed an underground centrifuge hall thought to have been the target of two US bunker-busters. The site was additionally struck by cruise missiles fired by a US submarine in the Arabian Sea.

Isfahan

Much of Iran’s mostly highly enriched uranium is thought to have been stored at the nuclear research and production centre near the city of Isfahan, the ancient capital of Safavid Persia.

International inspectors verified the fuel was there a fortnight ago, but satellite imagery suggests Iran may have moved it in recent days.

Israel had previously struck laboratories and three other buildings at the facility. The US did not use bunker-busters on Isfahan, which is thought to be mostly above ground, and instead attacked with cruise missiles.

The strikes are thought to have damaged six additional buildings, including a fuel rod production facility.

Overall assessment

A fuller picture of overall damage may emerge in the coming days, with experts urging caution about attaching too much credibility to the US president’s more optimistic pronouncements or to Iran’s defiant claims that its nuclear capacity remains largely intact.

Clionadh Raleigh, the head of the Armed Conflict Location and Event Data Project (ACLED), a conflict-monitoring group, warned that although the strikes might alter the timeline of Iran’s nuclear programme, they would do little to alter its ultimate trajectory.

“The regime’s broader power and intentions are likely to remain intact,” said Ms Raleigh.

“Iran’s military and intelligence systems are designed and built to survive. The structure is deeply layered and resistant to collapse. Even if key infrastructure is destroyed, the system adapts – and in some cases, becomes more dangerous in the process.

“There’s no evidence that the strikes will permanently end Iran’s pursuit of nuclear capabilities. What they may do is shift the timeline.”

Others were less cautious. Mick Mulroy, a former Pentagon official who served in the first Trump administration, told The New York Times that the US strikes will “likely set back the Iranian nuclear programme two to five years” – an assessment shared by Jason Brodsky of United Against a Nuclear Iran, a US-based pressure group.

The setback stems not only from the strikes themselves. Repairing the damage will be far harder following the assassination of more than a dozen nuclear scientists in the past 10 days, Israeli officials said.

“Several of the eliminated scientists had spent decades advancing nuclear weapons, constituting a significant part of the Iranian regime’s plans to annihilate the State of Israel,” one official said.

“These scientists had diverse professional expertise and extensive experience.”

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