After decades of threats, Israel on Friday launched an audacious attack on Iran, targeting its nuclear sites, scientists and military leaders.

Israeli Prime Minister Benjamin Netanyahu said the operation had “struck at the head of Iran’s nuclear weaponization program.”

But international assessments, including by the US intelligence community, say that Iran’s nuclear program isn’t currently weaponized. Tehran has also repeatedly insisted it isn’t building a bomb.

Still, that doesn’t mean it couldn’t if it chose to.

Iran has spent decades developing its nuclear program and sees it as a source of national pride and sovereignty. It maintains the program is solely for peaceful energy purposes and plans to build additional nuclear power plants to meet domestic energy needs and free up more oil for export.

Nuclear plants require a fuel called uranium – and according to the UN nuclear watchdog, no other country has the kind of uranium that Iran currently does without also having a nuclear weapons program.

That has fueled suspicions that Iran isn’t being fully transparent about its intentions. Tehran has used its stockpile of weapons-grade uranium as a bargaining chip in talks with the United States, repeatedly saying it would get rid of it if US-led sanctions are lifted.

So, what exactly is uranium’s role in a nuclear weapon, and how far is Iran from weaponizing its program? Here’s what you need to know.

When did Iran’s nuclear program start?

The US launched a nuclear program with Iran in 1957. Back then, the Western-friendly monarch – the Shah – ruled Iran and the two countries were still friends.

With backing from the US, Iran started developing its nuclear power program in the 1970s. But the US pulled its support when the Shah was overthrown during the Islamic Revolution in 1979.

Since the revolution, which transformed Iran into an Islamic Republic, Western nations have worried the country could use its nuclear program to produce atomic weapons using highly enriched uranium.

Iran has maintained that it does not seek to build nuclear weapons. It is a party to the UN’s Nuclear Non-Proliferation Treaty (NPT), under which it has pledged not to develop a bomb.

Here’s where its nuclear facilities are located.

Why is the program so controversial?

At the heart of the controversy over Iran’s nuclear program is its enrichment of uranium – a process used to produce fuel for power plants that, at higher levels, can also be used to make a nuclear bomb.

In the early 2000s, international inspectors announced that they had found traces of highly enriched uranium at an Iranian plant in Natanz. Iran temporarily halted enrichment, but resumed it in 2006, insisting it was allowed under its agreement with the UN’s nuclear watchdog, the International Atomic Energy Agency (IAEA).

It prompted years of international sanctions against Iran.

After years of negotiations, Iran and six world powers in 2015 agreed to a nuclear deal that limited Iran’s nuclear threat in return for lighter sanctions.

The deal required Iran to keep its uranium enrichment levels at no more than 3.67%, down from near 20%, dramatically reduce its uranium stockpile, and phase out its centrifuges, among other measures.

Uranium isn’t bomb-grade until it’s enriched to 90% purity. And nuclear power plants that generate electricity use uranium that is enriched to between 3.5% and 5%.

Does Iran have nuclear weapons?

It’s unclear how close Iran might be to actually building a nuclear bomb, if at all, but it has made significant progress in producing its key ingredient: highly enriched uranium. In recent years, it has sharply reduced the time needed to reach weapons-grade levels – now requiring just about a week to produce enough for one bomb.

In 2018, Trump pulled out of the Iran nuclear deal and initiated new sanctions on the regime to cripple its economy.

Tehran in turn said it would stop complying with parts of the agreement, and started increasing uranium enrichment and uranium stockpiles, and using advanced centrifuges.

It removed all of the IAEA equipment previously installed for surveillance and monitoring activities.

The Biden administration then kicked off more than a year of indirect negotiations with Iran aimed at reviving the deal, but those broke down in 2022.

In 2023, the IAEA said uranium particles enriched to 83.7% purity – close to bomb-grade levels – were found at an Iranian nuclear facility. Its stockpile of uranium enriched up to 60% had also grown to 128.3 kilograms, the highest level then documented.

And last year, the US shortened Iran’s so-called “breakout time” – the amount of time needed to produce enough fissile material for a nuclear weapon – “to one or two weeks.”

An IAEA report sent to member states late last month said Iran’s stock of 60% purity enriched uranium had now grown to 408 kilograms. That is enough, if enriched further, for nine nuclear weapons, according to an IAEA yardstick.

The IAEA has long accused Iran of violating its non-proliferation obligations, but on Thursday – for the first time in almost 20 years – its board passed a resolution officially declaring Iran in breach of those obligations. Iran promised to respond by escalating its nuclear activities.

What exactly is enriched uranium?

Enrichment is a process that increases the amount of uranium-235, a special type of uranium used to power nuclear reactors or, in much higher amounts, to make nuclear weapons.

Natural uranium is mostly uranium‑238 – about 99.3%, which isn’t good for power or bombs. Only about 0.7% is uranium‑235, the part needed to release energy.

For nuclear energy use, that tiny amount of useful uranium-235 needs to be concentrated. To do this, uranium is first turned into a gas, then spun at high speeds in machines called centrifuges. These machines help separate uranium-235 from the more common uranium-238. That is what enrichment is.

Uranium used in nuclear power plants is typically enriched to about 3.67%. To make a nuclear bomb, it needs to be enriched to around 90%. Iran has enriched uranium to 60% – not enough for a bomb, but a major step closer to weapons-grade material.

Centrifuges are essential for enriching uranium. The more advanced the centrifuge, the faster and more efficiently it can separate uranium-235 from uranium-238 – shortening the time needed to produce nuclear fuel or, potentially, weapons-grade material. Iran has spent decades improving its centrifuge technology, starting with its first-generation IR-1 model in the late 1980s. Today, it operates thousands of machines, including advanced models like the IR-6 and IR-9.

According to the Arms Control Association, Iran’s current centrifuge capacity could allow it to produce enough weapons-grade uranium for a bomb in less than two weeks.

How has Iran’s nuclear program been hit?

Israel says it’s targeting Iran’s nuclear infrastructure in its attack.

The nuclear complex there, about 250 kilometers (150 miles) south of the capital Tehran, is considered Iran’s largest uranium enrichment facility. Analysts say the site is used to develop and assemble centrifuges for uranium enrichment, a key technology that turns uranium into nuclear fuel.

The IAEA said three nuclear sites, Fordow, Isfahan and Bushehr, had not been impacted.

Six of Iran’s nuclear scientists were also killed in Israel’s strikes, Iranian state-affiliated Tasnim news agency said.

Some facilities are buried deep underground to put them out of reach of Israel’s weapons.

Shortly before sunrise in Iran on Friday, Israel launched the first strikes of its operation against the regime’s nuclear program.

That operation, called “Rising Lion,” had two prongs: Heavy airstrikes against at least one of Iran’s enrichment sites, and more targeted strikes in Tehran to decapitate the regime’s military leadership. It aimed to halt what Israel said was Tehran’s rapid progress in developing nuclear weapons.

Israel’s attack came after years of threats and days of heightened speculation – but without the United States’ blessing. The Trump administration stressed that Israel acted unilaterally and that Washington was “not involved.”

Israeli Prime Minister Benjamin Netanyahu said the operation would continue “for as many days as it takes” to eliminate Iran’s nuclear threat. Tehran, which insists its nuclear program is peaceful, says it has “no option but to respond.”

Here’s what you need to know.

Where and when did Israel strike?

Shortly after explosions rocked Tehran, Israel also struck elsewhere in the country. Israel’s military said it used jets to strike “dozens of military targets, including nuclear targets in different areas of Iran.”

An explosion was reported at Iran’s main enrichment facility in Natanz, about 250 kilometers (150 miles) south of Tehran.

The United Nations’ nuclear watchdog, the International Atomic Energy Agency (IAEA), confirmed that Natanz had been hit, but said it had not observed an increase in radiation levels in the area.

Rafael Grossi, the head of the IAEA, said other nuclear facilities in Iran – Isfahan, Bushehr and Fordow – were not impacted. The Fordow site is buried under a mountain, and is considered a much harder target for Israel.

What did Israel say?

In a televised address, Netanyahu said Israel had taken action to “roll back the Iranian threat to Israel’s very survival,” and said it would continue its operation for as long as it takes “to remove these threats.”

Netanyahu claimed that Iran had in recent years produced enough highly enriched uranium for nine nuclear weapons.

“Iran could produce a nuclear weapon in a very short time. It could be a year, it could be within a few months,” he said. “This is a clear and present danger to Israel’s survival.”

The Israel Defense Forces (IDF) also said it had destroyed Iran’s ballistic missile launch sites and stockpiles.

Who did Israel kill?

Several of the most important men in Iran’s military and its nuclear program were killed in Israel’s strikes.

Maj. Gen. Hossein Salami, head of the secretive Islamic Revolutionary Guard Corps (IRGC), was the highest-profile of those killed.

Israel also said it killed Maj. Gen. Mohammad Bagheri, chief of staff of Iran’s armed forces; Ali Shamkhani, a close aide to Iran’s Supreme Leader Ayatollah Ali Khamenei; and Ali Hajizadeh, commander of the IRGC’s air force.

How might Iran hit back?

Iran’s retaliation has already begun. The IDF said Tehran has fired more than 100 drones toward Israel and that Israeli defenses were working to intercept the drones.

Iran’s President Masoud Pezeshkian urged the Iranian people to remain unified and trust Iran’s leadership.

“The nation needs unity… more than ever,” he added.

After a series of lethal and embarrassing Israeli blows against the Iranian regime, it is not clear how Tehran might attempt to exact retribution.

Following previous Israeli attacks against Iran and its proxies in the region, Tehran fired back with huge salvos of ballistic missiles.

The Institute for the Study of War, a think tank in Washington DC, said this time it was “possible that Israel somehow disrupted Iran’s response by targeting Iran’s ballistic missile launch sites and stockpiles.”

How has the US responded?

The Trump administration – which has been pursuing a diplomatic path with Iran in recent weeks – sought to distance itself from Israel’s attack.

Secretary of State Marco Rubio said Israel’s actions were “unilateral.” Although Israel notified the US ahead of its strikes, Rubio said the US was “not involved” in the attack.

“Our top priority is protecting American forces in the region,” he added. Earlier this week, the US had made efforts to arrange the departure of non-essential personnel from various countries in the Middle East, leading to speculation that an Israeli attack on Iran could be imminent.

US President Donald Trump urged Iran to agree to a new nuclear deal “before there is nothing left,” suggesting that follow-up Israeli attacks on the country would be “even more brutal.”

Trump said he had given Iran “chance after chance” to make a deal. “JUST DO IT, BEFORE IT IS TOO LATE,” he wrote on Truth Social, his social media platform.

What happened to the last Iran nuclear deal?

Under a 2015 nuclear deal struck by former US President Barack Obama, formally known as the Joint Comprehensive Plan of Action (JCPOA), Iran agreed to drastically limit its number of centrifuges and cap uranium enrichment at levels far below those required to make weapons, in exchange for sanctions relief.

But during his first term as president in 2018, Trump withdrew from the JCPOA, saying the “rotten structure” of the agreement was not enough to prevent Iran from developing a nuclear bomb. He ramped up sanctions on Iran and threatened to sanction any country that helped the regime to obtain nuclear weapons.

In his second term, Trump has revived efforts to strike a new nuclear deal with Iran. Just hours before Israel’s strikes, the president cautioned Israel against launching an attack while US-Iran talks are ongoing.

“As long as I think there is an agreement, I don’t want them going in because that would blow it. Might help it, actually, but also could blow it,” Trump said.

In the face of Israel’s far-reaching strikes Friday, it’s not clear that Iran – its longtime foe – has the capacity to muster the furious response that might be expected.

Israel has once again demonstrated it is the pre-eminent military and intelligence power in the Middle East, heedless to civilian casualties and the diplomatic impact of its actions on its allies.

As with their remarkable operation to decapitate their northern opponent – the Iranian proxy in Lebanon, Hezbollah – the overnight operation has the hallmarks of months or even years of preparation. And Prime Minister Benjamin Netanyahu may have been faced with using this capability now, or losing it, as diplomacy kicked in during a sixth round of nuclear talks scheduled for this weekend between the United States and Iran in Oman.

Iran is now left counting its far-reaching wounds. Images from across Tehran show apartment blocks hit, it seems, in specific rooms – suggesting the pinpoint targeting of individuals, likely through tracking cellphones. Iran has lost its top three active-duty commanders, as well as a leading voice in nuclear talks, overnight, but as the dust clears it may emerge more have been hit, and the survivors will likely be concerned they, too, could still be targeted.

This will slow and complicate any Iranian response. As will the damage the Iranians continue to sustain. A raid by Israel in October took out a large tranche of Iran’s air defenses. Israel’s military said Friday that it had destroyed dozens of radars and surface-to-air missile launchers in strikes by fighter jets on aerial defense arrays in western Iran. The Iranian atomic energy agency confirmed that the nuclear enrichment facility at Natanz had also been damaged, but it’s not yet clear to what extent.

In the days ahead, Israel’s superior intelligence apparatus will search for targets of opportunity – commanders and equipment changing location, or the movement of materiel to facilitate a response – and continue to strike.

Such a wide-ranging assault was possible only because Hezbollah – Iran’s second-strike capability if their nuclear apparatus was hit – had been dismantled over a ruthless but effective months-long campaign last summer. This is beginning to look like a months-long Israeli plan to remove a regional threat.

The risks remain high. Iran could now try to race for the nuclear bomb. But its faltering defenses and clear, humiliating infiltration by Israel’s intelligence, make that a long shot. Rushing to build a nuclear weapon is no simple task, especially under fire, with your key leadership at risk of pinpoint strikes. Netanyahu may have calculated that the risk of an Iranian nuclear breakout was depleted, and manageable with yet more military might.

There is another victim of the overnight barrage: the Trump administration’s standing as a geopolitical power.

There may be suggestions from Trump advocates in the hours ahead that the Israeli assault was part of a wider masterplan to weaken Iran ahead of more diplomacy. But, in reality, a simpler truth is revealed: Israel had no trust in the United States to implement a deal with Iran that would remove its nuclear ambitions.

Despite public pleading by US President Donald Trump for it to hold off, Israel went ahead with the most significant attack on Iran since its war with Iraq in the 1980s. Israel neither cared for or feared Trump’s response, and is apparently prepared to risk fighting on without US support.

That is perhaps another indictment of Iran’s ability to respond now. Israel is less bothered by what it can do. Israel’s operation against Hezbollah provides reason for it to be confident (but also should stir anxieties about hubris and overreach). Israel has likely hit the vast majority of its key targets already, to maximize the advantage of surprise, and the extent of that damage will take days to be revealed.

What of proliferation now? There is a lot that we do not know about Iran’s nuclear program. Israel may have known a lot more. But we are now in a binary moment where the strikes on the Natanz facility may either herald its end, or its race to completion – in the form of a nuclear weapon. Iran has always insisted its nuclear program is peaceful, but the United Nations’ nuclear watchdog on Thursday declared it in breach of its non-proliferation obligations, prompting Tehran to promise escalatory action.

In the moment of its greatest weakness, the Islamic Republic will struggle to project the regional swagger it has maintained for decades. It may feel it is unable to grasp diplomacy with the US as its way out, without looking even weaker. It appears unable to hit Israel back proportionately, so may look to strike asymmetrically, if possible.

In the immediate confusion, one basic fact is clear: Israel is acting in the Middle East now unimpeded by allies, unafraid of wider risks, and – at times brutally – seeking to alter regional dynamics for decades to come.