Behind the bombs: How Iran’s nuclear program brought it to the brink with Israel | Explained

A day before Israel’s attack, the IAEA formally declared Iran in breach of its non-proliferation obligations for the first time in 20 years. 19 of the 35 countries on the board of IAEA voted for the motion, which was backed by the US, UK, Germany and France.

The resolution said Iran has failed to fully answer the UN nuclear watchdog’s questions about hidden nuclear material and past activities, which counts as a violation. It also raises concern over Iran’s growing stockpile of enriched uranium, which can be used for both energy and nuclear weapons. In response, Iran called the resolution political and announced it would open a new uranium enrichment site.

An IAEA report last week criticised Iran for its "general lack of co-operation" and said it now has enough 60% enriched uranium – close to weapons-grade – to potentially build nine nuclear bombs.

Iran denies any intention to build nuclear weapons, insisting its program is peaceful.

Under the 2015 nuclear deal with world powers, Iran agreed to limit its nuclear work, allow strict IAEA inspections, and help resolve past concerns in exchange for sanctions relief.

These concerns have heightened global fears that Iran is no longer just a threshold nuclear state, but one that could cross the line at any moment, especially amid growing regional instability.

Why Iran violated the nuclear deal: The breakdown of JCPOA

The Joint Comprehensive Plan of Action (JCPOA) was signed in 2015 between Iran and world powers – US, UK, France, Germany, Russia, and China. Under the deal, Iran agreed to strictly limit its uranium enrichment, reduce its centrifuge numbers, and allow intrusive IAEA inspections, in exchange for relief from international sanctions.

But in 2018, the US under President Donald Trump unilaterally withdrew from the deal, calling it “the worst agreement ever negotiated” and reimposed crippling sanctions.

Iran responded gradually, and then aggressively, by violating JCPOA terms by restarting enrichment at higher levels, installing advanced centrifuges, blocking IAEA access, and building up stockpiles well beyond allowed limits.

Efforts to revive the JCPOA since 2021 have stalled, and with hardliners dominating Iran’s leadership, Tehran has shown little interest in returning to full compliance. Israel, which always viewed the JCPOA as flawed, now sees the collapse of the deal as proof of its long-held fears: Iran cannot be trusted to play by the rules.

Inside Iran’s nuclear facilities

Iran’s nuclear program is vast, deeply entrenched, and heavily fortified, spread across multiple sites, some of which are declared, while others are suspected.

At the centre of this network is the Natanz facility – the country’s primary uranium enrichment site – which was targeted by Israel in its airstrikes on Friday. Natanz houses thousands of IR-1 and advanced IR-6 centrifuges and has long been a focal point of international concern due to its capacity to enrich uranium rapidly.

Another critical site is Fordow, built deep inside a mountain near Qom, which was originally secret and is now used to enrich uranium to high levels of purity, including up to 60%. This facility’s deeply buried structure makes it especially difficult to target militarily.

Beyond these, the Arak heavy water reactor, originally intended for plutonium production, remains under watch despite modifications agreed upon under the nuclear deal. Additional facilities in Isfahan, Bushehr, and the Tehran Research Reactor contribute to fuel production, research, and medical isotope development. Together, these sites form the backbone of Iran’s nuclear program — a mix of civilian infrastructure and capabilities that the West and Israel fear could be repurposed for a covert nuclear weapons effort.

What makes Iran’s nuclear ambitions controversial

Iran maintains that its nuclear program is purely peaceful, aimed at generating electricity and advancing medical research. However, several factors have led to deep international suspicion.

First, Iran’s nuclear history includes evidence of past weapons-related research, with US and IAEA assessments concluding that the country conducted secret weapons development work at least until 2003. Iran has yet to fully account for these so-called "possible military dimensions" of its program.

Second, its repeated lack of transparency, including limiting access to IAEA inspectors and removing surveillance cameras from key facilities, has raised concerns about hidden activities.

Compounding the issue is Iran’s continued development of ballistic missiles, some with ranges capable of carrying a nuclear payload, even though Tehran denies any such intent.

The regional security context also adds to the unease: Iran backs armed proxies like Hezbollah and the Houthis, and its adversaries fear that a nuclear-armed Iran would embolden these groups and destabilize the Middle East further.

Perhaps most alarming is Iran’s growing "breakout capability" — its ability to rapidly produce weapons-grade uranium. Experts now estimate Iran could achieve this in a matter of weeks, and while it hasn’t yet weaponised its stockpile, that technical gap is narrowing. Together, these elements make Iran’s nuclear ambitions not just controversial but potentially explosive on the world stage.