“Half a Mile Underground”: Iran’s Nuclear Bunkers Could Survive First Strike, Warns IAEA Chief

(DEFENCE SECURITY ASIA) – The head of the United Nations’ nuclear watchdog has issued a stark warning that Iran’s most sensitive nuclear facilities are buried so deep underground that they cannot be eliminated by a single airstrike, reinforcing concerns about the growing complexity of any future military option.

Rafael Grossi, Director-General of the International Atomic Energy Agency (IAEA), told The Financial Times that, “The most sensitive things are half a mile underground (about 800 meter) — I have been there many times,” adding, “To get there you take a spiral tunnel down, down, down.”

His remarks come amid heightened fears that the breakdown of nuclear negotiations could tip the region into a catastrophic conflict, with Grossi cautioning, “The Iranian thing has incredible potential to become catastrophic. If there is a failure in negotiation, this will imply most probably military action.”

Grossi underscored that while Iran does not yet possess a nuclear weapon, it has already stockpiled enough enriched material to move dangerously close to that threshold.

“Iran doesn’t have a nuclear weapon at this moment, but it has the material,” he said in the same interview, reinforcing concerns shared by Western intelligence agencies.

The Islamic Republic’s nuclear programme is distributed across multiple fortified sites, meaning any pre-emptive military strike would need to simultaneously target a broad range of facilities to achieve meaningful degradation.

IAEA officials admit that they are not fully aware of the whereabouts of certain crucial nuclear components, including advanced centrifuge parts used to enrich uranium to weapons-grade levels.

Military analysts assess that Israel could potentially mount a limited strike on key facilities, but the effort would require multiple sorties and would need to overcome layered air defences, including Russian-supplied surface-to-air missile systems, like the S-300 series, currently active in Iranian airspace.

Indeed, Israel has demonstrated its ability to evade Iranian air defences in limited operations, but replicating that across deeply buried, dispersed nuclear sites would significantly increase operational risk and complexity.

At the centre of Iran’s enrichment effort lie two hardened sites: the Natanz Fuel Enrichment Plant, located around three storeys underground, and the Fordow facility, which is buried even deeper within a mountain — both designed to resist aerial bombardment.

While Israel’s arsenal includes 5,000-pound bunker buster munitions, analysts argue these would be insufficient against the deeply entrenched Fordow site without a sustained and coordinated air campaign.

Only the United States, with its 30,000-pound (14,000 kg) Massive Ordnance Penetrator (MOP), currently deployed on B-2 stealth bombers, can credibly threaten such deeply buried targets — a fact that has gained renewed relevance with the recent movement of B-2 aircraft to Diego Garcia in the Indian Ocean.

“[Israel] doesn’t have enough 5,000 pounders,” noted retired U.S. Air Force General Charles Wald, now with the Jewish Institute for the National Security of America, highlighting that any solo Israeli action would be slow, complex, and far less effective.

Wald noted that a joint U.S.-Israeli operation would have a greater chance of success, though even that would not eliminate Iran’s nuclear ambitions outright and could take several days to execute.

The U.S. Air Force’s forward positioning of B-2 bombers, capable of deploying MOPs against ultra-hardened targets, serves as a calculated strategic message to Tehran — a reminder of the options on the table should diplomacy fail.

However, nuclear analysts caution that even a powerful strike could only set back, not eliminate, Iran’s nuclear capabilities.

“A strike by the United States could probably cause more damage than an Israeli strike, but in either case you’re talking about buying time and there’s a real risk that it drives Iran toward rather than away from a bomb,” said Eric Brewer of the Nuclear Threat Initiative and former U.S. intelligence analyst.

Experts widely agree that military force could delay Iran’s progress but cannot erase the scientific knowledge or domestic industrial base behind its nuclear programme.

“What happens the day after? Iran responds to attacks on its nuclear program by hardening its facilities and expanding its program,” said Kelsey Davenport of the Arms Control Association, noting that efforts to prevent reconstruction would be extremely resource-intensive.

The strategic implications of any attack are far-reaching, particularly as Iran has already revoked the additional transparency and verification measures agreed under the 2015 nuclear accord.

A military confrontation would likely prompt Tehran to expel IAEA inspectors and halt remaining cooperation with international nuclear oversight bodies, effectively blinding the global community.

“The continuation of external threats and Iran being in a state of military attack may lead to deterrent measures, including expulsion of inspectors from IAEA and cessation of cooperation,” warned Ali Shamkhani, a senior adviser to Supreme Leader Ayatollah Ali Khamenei, in a social media post last week.

Such a move would echo North Korea’s past actions — a country that, after expelling IAEA inspectors, went on to successfully test nuclear weapons.

“If you bomb Iran, Iran is going to almost certainly in my judgement chuck out international inspectors, make a dash for the bomb,” warned James Acton of the Carnegie Endowment for International Peace, echoing a growing chorus of voices warning against the unintended consequences of pre-emptive military action.

As the Middle East simmers with overlapping crises — from Gaza and Lebanon to Houthi missile attacks in the Red Sea — any escalation involving Iran’s nuclear facilities could ignite a wider regional conflagration, drawing in global powers and reshaping the security architecture of the entire region.

In this high-stakes geopolitical chessboard, any miscalculation could shift the region from a precarious balance of deterrence to full-blown confrontation.

— DEFENCE SECURITY ASIA