From US-built reactors to secret enrichment sites and global standoffs, this comprehensive explainer breaks down the key moments that shaped Iran’s nuclear program and why it matters now more than ever.
Click here to read the full story.
From US-built reactors to secret enrichment sites and global standoffs, this comprehensive explainer breaks down the key moments that shaped Iran’s nuclear program and why it matters now more than ever.
Click here to read the full story.
Iranian officials insist the program is peaceful, but Tehran's uranium enrichment expansions have concerned Western powers and led to warnings from Israel and the United States of possible military action.
When and why did Iran start its nuclear program?
Iran's nuclear activities began in the 1950s under Shah Mohammad Reza Pahlavi as one component of a US-supported initiative to promote civilian nuclear power in allied nations. The United States helped Iran build its initial research reactor at Tehran University under the Atoms for Peace initiative. The shah envisioned a grid of reactors to power Iranian cities, coupled with enhancing the scientific stature of the country.
Iran had by the 1970s signed with France and West Germany a deal to build a number of reactors. America had in principle agreed to allow Iran to establish a full nuclear fuel cycle, including uranium enrichment and reprocessing — technology that is sensitive as it could be used to produce fuel for civilian reactors or weapons.
Western countries considered Iran a reliable ally at the time, and little global outcry was expressed over the program. That all changed with the Islamic Revolution in 1979.
What happened to the program after the Islamic Revolution?
When the shah was overthrown and Ruhollah Khomeini established the Islamic Republic, most of Iran's nuclear activities came to a halt. Foreign suppliers stepped back. Several nuclear facilities were abandoned or left unfinished. Iran's new leaders, wary of Western influence and burdened with war against Iraq, relegated nuclear development to the bottom of their agenda.
But by the late 1980s and early 1990s, Iran began to restart its program. The Islamic Republic signed agreements with Russia and Pakistan and ramped up activity at facilities like Natanz and Arak. These efforts raised suspicions, especially because Iran was operating some of its facilities clandestinely.
The IAEA was not aware of all the construction, and suspicions mounted about whether Iran's intentions were strictly civilian or not.
What contributed to the nuclear standoff?
The dissident opposition group National Council of Resistance of Iran revealed in 2002 two secret Iranian nuclear sites at Natanz and Arak. The revelation shocked Western intelligence and led to a request by the UN nuclear watchdog agency, the International Atomic Energy Agency (IAEA), for an inquiry.
Inspectors confirmed the existence of indications that Iran had conducted activity pertinent to acquiring a nuclear weapon — such as experiments on high-explosives and possible models for missile warheads.
Iran said it intended to acquire only nuclear power and not an atomic bomb. Yet its concealment of the operations from reporting contravened Iran's safeguards treaty to the Nuclear Non-Proliferation Treaty (NPT) that it had signed.
As a counter, the UN Security Council imposed a set of resolutions that insisted Iran stop suspending its reprocessing and enrichment. Sanctions were enforced upon Iran's defense, energy, and banking. The confrontation hardened over the decade that followed.
What was the purpose of the 2015 nuclear accord?
After years of negotiations, Iran and six of the world's top powers — US, UK, France, Germany, Russia, and China — agreed on the Joint Comprehensive Plan of Action (JCPOA) in July 2015.
Under the deal, Iran agreed to restrict uranium enrichment to 3.67% purity — well short of weapons-grade. The deal also limited Iran's partially enriched uranium stockpile to 300 kilograms. It dismantled and stored thousands of centrifuges. It agreed to intrusive IAEA inspections such as supply chain tracking and declared facilities.
In return, Iran gained relief from international sanctions, including the unfreezing of billions in foreign assets and re-entry into international oil markets.
The US administration's allies greeted the deal as a major non-proliferation achievement. President Barack Obama called it "a long-term deal that will prevent Iran from obtaining a nuclear weapon."
The United States why pulled out of the deal?
The United States withdrew from the 2015 Iran nuclear deal in May 2018, when then-President Donald Trump announced that the agreement had failed to prevent Iran from expanding its ballistic missile program or aiding armed groups across the region.
Announcing the deal "a disaster," Trump reimposed sweeping sanctions in what his administration described as a "maximum pressure" campaign to push Iran to accept more restrictive terms.
“Iran’s leaders will naturally say that they refuse to negotiate a new deal. That’s fine. I’d probably say the same thing if I were in their position. But the fact is, they’re going to want to make a new and lasting deal,” Trump said at the White House at the time of the withdrawal announcement.
The International Atomic Energy Agency (IAEA) confirmed in a series of quarterly reports that Iran remained in compliance throughout the remainder of Trump's term — including May, August, and November 2018 inspections, as well as early 2019.
Tehran's gradual erosion of the accord came only after Joe Biden's election. On January 4, 2021, just over two weeks before Biden took office, Iran resumed 20% enrichment at its Fordow plant. In February, it prevented IAEA inspectors from visiting its facilities and began producing uranium enriched to 60% by mid-April — far beyond the limit of the accord's 3.67%, but short of the 90% necessary for weapons-grade material.
Iran currently has a reserve of enriched uranium above the Joint Comprehensive Plan of Action (JCPOA) threshold, enriched to 60% purity, according to the IAEA.
Although Biden officials have spoken of Trump's withdrawal as the trigger for the deal's collapse, timelines show that Iran did not commit serious violations until the end of Trump's presidency.
How close is Iran to developing a nuclear weapon?
According to US intelligence estimates Tehran is now able to produce enough highly enriched uranium for a single nuclear weapon within weeks if it were to decide to do so.
In a recent TV interview, Ali Larijani, the Supreme Leader's chief adviser warned that Iran will be able to make weapons if pushed into a corner. “If you make a mistake regarding Iran’s nuclear issue, you will force Iran to take that path, because it must defend itself,” he said.
The IAEA has expressed concern about traces of uranium that remain unidentified at undeclared locations and reports that Iran has not provided sufficient explanations on a number of issues that remain outstanding.
What is the official position of Iran?
Iran continues to say that its nuclear program is peaceful. "The official stance of Iran in rejecting weapons of mass destruction and regarding the peaceful nature of the Islamic Republic’s nuclear program is clear," foreign ministry spokesman Esmail Baghaei said.
But officials generally follow such statements with warnings regarding self-defense. Baghaei cited a recent speech of the Supreme Leader to the effect that Iran would arm itself "to the extent necessary for the defense of Iran."
Iranian leaders present the US and Israel as the aggressors. "The enmity from the US and Israel has always been there. They threaten to attack us, which we don’t think is very probable, but if they commit any mischief, they will surely receive a strong reciprocal blow," Khamenei said in March 2025.
Why are the US and Iran negotiating now?
US and Iranian officials conduct talks in Oman hoping to revive the nuclear talks. The discussions, President Trump announced, will be direct, while Iranian Foreign Minister Abbas Araghchi announced that communication would be through intermediaries.
The diplomatic push coincides with rising tensions. Trump has sent a letter to Khamenei threatening to punitive military strikes if there is no deal. “I’ve written them a letter saying, ‘I hope you’re going to negotiate because if we have to go in militarily, it’s going to be a terrible thing,’” Trump said.
What is Israel's role in the nuclear standoff?
Israel has always opposed the JCPOA and sees a nuclear Iran as an existential threat. Israel is believed to have orchestrated sabotage plots against Iranian nuclear facilities and assassinations of Iranian nuclear scientists in the last two decades, based on intelligence officials quoted by several Western news outlets.
Although Israel has not publicly taken responsibility of all the incidents, it has committed to acting if diplomacy fails. Iran has, in turn, correlated its nuclear stance with the danger of Israel's undeclared nuclear capacity and record of strikes.
What's on the line now?
With Iran's uranium enrichment to new record levels and diplomacy at an impasse, the threat of escalation hangs perilously close. The deployment of US B-2 bombers to the region, as well as Tehran's threat to employ its underground cities of missiles as a counter-attack, is what accentuates the mounting tension. The crisis has been amplified by further incendiary language against Iran from Donald Trump.
Both sides still express a preference for negotiation, but there is profound mutual distrust. America wants tighter terms; Iran demands sanctions relief and guarantees the deal won't collapse like before.
The success of current efforts has the potential to decide not just Iran's nuclear future but the broader dynamics of Middle Eastern security for decades to come.
Supreme Leader Ali Khamenei's oft stated mantra of "no war and no negotiations" with the United States became untenable when US President Donald Trump gave a stark ultimatum that he reach a nuclear deal or face attack.
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