Iran talks nukes, but how close is it to building one?

Tehran has warned that any attack by the US or its allies could push it to pursue nuclear weapons

Technicians work at the Arak heavy water reactor's secondary circuit, about 300km south-west of Tehran. AP

Iran has warned that any attack by the US or its allies could push Tehran to pursue nuclear weapons, reversing its long-held stance against developing atomic military capabilities.

As tensions in the Middle East escalate and Iran’s nuclear capabilities advance amid a US “maximum pressure” campaign, many in the region and beyond are again forced to consider a long-dreaded question: Is Iran nearing the nuclear threshold, and what can be done to stop it?

Here is a breakdown of the key components of Iran’s nuclear programme and the possible scenarios:

What is Iran’s nuclear programme composed of?

Iran’s nuclear infrastructure is built primarily around uranium enrichment, with the ultimate aim of either fuelling civilian reactors, or, if it chooses, rapidly building nuclear weapons. As of early 2025, Iran is operating at an unprecedented level of activity.

According to experts, Iran runs 36 cascades of IR-1 centrifuges and 42 cascades of advanced machines – IR-2m, IR-4, and IR-6 – at the Natanz Fuel Enrichment Plant (FEP). Another 13 cascades of IR-1 and IR-6 centrifuges are operating at Fordow, a facility buried deep in the mountains. Additional centrifuge arrays are spinning at the Natanz pilot plant.

Although none of Iran’s centrifuges are currently enriching uranium to the 90 per cent level that defines weapons-grade material, it already has a stockpile enriched to 60 per cent, according to the Washington-based Institute for Science and International Security. With further enrichment, that material could fuel up to eight nuclear warheads.

Moreover, Iran has produced small quantities of uranium metal, a material that can substitute for weapon-grade cores, at the Esfahan Nuclear Technology Centre. The institute reported that Iran has “accomplished a considerable amount” of preparatory work for weaponisation.

Where are the main nuclear sites and how are they protected?

Iran’s nuclear facilities are widely dispersed and increasingly fortified against attack.

Natanz, located 225km south of Tehran, is Iran’s flagship enrichment site. According to the James Martin Centre for Nonproliferation Studies, the centre now includes four tunnels bored into the Kuh-e Kolang Gaz La, or “Pickaxe Mountain”, providing underground protection against air strikes.

Fordow, a heavily reinforced plant embedded in a mountain near Qom, was a former Islamic Revolutionary Guard Corps base whose existence was kept secret until 2009. The institute described it as “already a hardened structure” at that time, built specifically to withstand attack.

Other key centres include Arak, Esfahan and Parchin, the latter of which is a sprawling military research laboratory linked to explosives testing and missile development.

Arak, one of Iran's key nuclear enrichment centres. AFP

Iran has invested heavily in multi-layered air defence systems to protect these sites. In January, Tehran claimed it shot down a simulated Israeli bunker-buster bomb using a Dey-9 missile, during drills simulating an attack on Natanz. Iran’s air defences include Russian-built TOR systems, and it claims to have modified them to target bombs rather than just aircraft or missiles.

However, aviation experts who spoke to The National stated that these drills probably occurred under test conditions and would not reflect the chaos of actual conflict. They warned that even the successful interception of a bomb does not mean the defence system could survive long enough to engage it during a real-world strike, especially against Israeli electronic warfare and decoy systems.

How close is Iran to building a nuclear weapon?

The most urgent question is whether Iran has crossed the so-called “breakout threshold”.

According to the Council on Foreign Relations think tank, Iran could produce enough fissile material for one weapon in a matter of weeks, a drastic shift from the one-year estimate embedded in the 2015 nuclear deal, the Joint Comprehensive Plan of Action. That deal was designed to provide world powers with reaction time. However, after the US withdrew from it in 2018, Iran gradually ramped up enrichment and restricted inspections. The last full International Atomic Energy Agency inspection occurred in 2021.

Last June, former US Secretary of State Antony Blinken warned Iran could now produce weapons-grade material in “one or two weeks”. However, analysts stress that producing fissile material is only the first step. Weaponisation involves building the device, ensuring it works reliably and integrating it into a delivery system. This process could take several more months, particularly if Iran wants to field an initial arsenal, not just a single device.

Can the US or Israel strike Iran’s nuclear centres?

The US and Israel have long maintained that they will not allow Iran to obtain nuclear weapons. But mounting an effective strike would be complex and risky.

To effectively neutralise such targets, the US would likely consider using specialised munitions like the GBU-57 Massive Ordnance Penetrator (MOP), a 30,000-pound bomb capable of penetrating deep into the earth to destroy subterranean centres.

An engineer inside Iran's Natanz uranium enrichment plant. AFP

Israel’s most powerful bomb, the GBU-28, is capable of penetrating some bunkers but not deep enough for targets buried under mountains. The much larger GBU-57, the only bomb designed to destroy ultra-hardened targets, requires B-2 or B-1 bombers, which only the US possesses.

Israel has used covert tactics in the past: cyberattacks like Stuxnet in 2010, assassinations of nuclear scientists such as Mohsen Fakhrizadeh in 2020 and sabotage at Natanz. However, direct strikes on hardened centres like Fordow are another matter.

Even if Israel were to attempt a strike with its F-15I fighter bombers, it would face serious logistical challenges, including the need to refuel mid-air for long-range flights. Iran’s air defences, radar systems and electronic warfare countermeasures would pose further obstacles. Israel might also use stealth F-35s, decoy drones like the ATALD, and HARM missiles to suppress radar. But success is not guaranteed.