The 2015 nuclear deal let Iran enrich uranium to 3.67 percent. In April 2021, Tehran announced it was making 60 percent. That jump, and what followed it, is the core of the standoff over Iran’s program.
The cap and the breach
The Joint Comprehensive Plan of Action was reached on July 14, 2015, and took effect on January 16, 2016. Germany, France, the United Kingdom, the United States, Russia, China and Iran were all party to it. Iran agreed to curtail its program, and sanctions relief was the payoff. The Arms Control Center notes that the enrichment cap of “3.67% until 2030” was paired with “sunset provisions”: limits on centrifuges lapsed after 10 years, and enrichment restrictions eased after 15.
Washington walked out in 2018. The German Federal Foreign Office says Iran then gradually dropped its obligations, raised enrichment to as high as 60 percent and cut back the access of International Atomic Energy Agency inspectors. In February 2021 Iran suspended the Additional Protocol.
The sequence was staged. According to SIPRI, Iran reached just under 20 percent (around 19.5 per cent) in December 2020, then announced 60 percent at the Pilot Fuel Enrichment Plant at Natanz in April 2021. Ali Akbar Salehi put the rate at “9 grams per hour, or about 1 kilogram every five days.” The announcement came during the Vienna talks on rescuing the deal, and Tehran framed it as a reply to sabotage at its underground enrichment site.
Why 60 percent matters
SIPRI is careful here. Uranium at 60 percent “cannot be used to make a useful nuclear explosive device,” the essay says. Weapons-grade is 90 percent, though, and the last stretch is short, potentially about a week. The essay reads the choice as a political message: “We have gone as far as we can go in response to provocations without producing weapons-grade uranium.”
The stockpile has kept growing. The Arms Control Center puts Iran’s 60 percent material at 182 kg in October 2024, 275 kg in February 2025 and “over 400 kg” by May 2025, nearly 50% more in three months. Estimated breakout time fell from “more than one year” under the deal to “one week or less.”
Inspections and talks
The German Foreign Office states that Iran is the only non-nuclear-weapon state in the Non-Proliferation Treaty to have enriched uranium that far. About 440 kilograms of highly enriched uranium is unaccounted for, enough, it says, to “provide enough material to produce ten nuclear weapons” if enriched further. Since June 2025 Iran has blocked inspections at Natanz, Isfahan and Fordow.
In August 2025 Germany, France and the United Kingdom triggered the snapback mechanism, restoring UN Security Council resolutions that call for a complete ban on enrichment and strict IAEA inspections.
Diplomacy ran in parallel. Oman mediated five rounds between Washington and Tehran from April to June 2025. The U.S. floated a regional consortium in neighboring countries in place of enrichment on Iranian soil. Iran rejected that and called enrichment inside Iran non-negotiable.
Sources
- Why is Iran producing 60 per cent-enriched uranium? (SIPRI)
- The Iran Deal, Then and Now (Arms Control Center)
- Iran's nuclear programme (German Federal Foreign Office)
