History of Iran’s nuclear program: Timeline

What Happened

• An interim accord signed on 17 June 2026 (the "Islamabad Memorandum") between the US and Iran aims to end the West Asia war that began on 28 February 2026 and pave the way for a broader settlement of Iran's decades-long nuclear dispute.
• The deal provides a 60-day negotiation window to address Iran's nuclear programme, particularly the disposition of its enriched uranium stockpile and future enrichment ceilings.
• Understanding the historical arc of Iran's nuclear programme — from its civilian origins in the 1950s through clandestine enrichment, the 2015 JCPOA, the US withdrawal, and the collapse into conflict — is essential context for evaluating the MoU's prospects.

Static Topic Bridges

Phase 1: Civilian Beginnings under the Shah (1957–1979)

Iran's nuclear programme began under the "Atoms for Peace" initiative launched by US President Dwight D. Eisenhower in 1953, which aimed to share peaceful nuclear technology with allied nations. In 1957, the US and Iran signed a civil nuclear cooperation agreement. Iran signed the NPT in July 1968 (ratified by Parliament in February 1970). The Tehran Research Reactor (TRR) was supplied by the US and went operational in 1967. The Atomic Energy Organisation of Iran (AEOI) was established in 1974. The Bushehr Nuclear Power Plant (on the Persian Gulf coast, Bushehr Province) was begun with German assistance in 1975 but was abandoned after the 1979 Islamic Revolution.

Phase 2: Clandestine Development and IAEA Discovery (1988–2003)

Following the Iran–Iraq War (1980–88), Iran resumed nuclear activities with assistance from Pakistan's A.Q. Khan network (centrifuge technology supplied covertly from the 1980s) and Russia (Bushehr restart agreement, 1992). In August 2002, the exiled group Mujahedin-e-Khalq (MEK) publicly revealed that Iran had been secretly constructing an enrichment facility at Natanz (Isfahan Province) and a heavy water plant at Arak — neither declared to the IAEA. This triggered an IAEA inspection process. Iran signed the Additional Protocol in December 2003, agreeing to broader inspections, and voluntarily suspended enrichment.

Phase 3: Escalation and Sanctions (2006–2013)

After voluntarily suspending enrichment in 2003, Iran resumed enrichment at Natanz in January 2006, ending the suspension. In April 2006, President Ahmadinejad announced Iran had enriched uranium to reactor grade using 164 centrifuges. The UN Security Council adopted multiple resolutions imposing sanctions (UNSC Resolutions 1737 in 2006, 1747 in 2007, 1803 and 1835 in 2008, and 1929 in 2010). In 2010, Iran announced it had begun enriching to 20% HEU. In 2011, the IAEA reported evidence of "possible military dimensions" to Iran's programme. Multiple rounds of EU, US, and UN sanctions steadily tightened. In 2010, the Stuxnet cyberattack (attributed to the US and Israel) destroyed approximately 1,000 Iranian centrifuges at Natanz.

Phase 4: The JCPOA — Joint Comprehensive Plan of Action (2015–2018)

After election of moderate President Hassan Rouhani in 2013, a diplomatic track re-opened. On 14 July 2015, Iran and the P5+1 (US, Russia, China, UK, France + Germany, also called E3+3) signed the Joint Comprehensive Plan of Action (JCPOA) in Vienna. UNSC Resolution 2231 (adopted 20 July 2015) endorsed the JCPOA. Key provisions: Iran's enrichment capped at 3.67%, centrifuge count reduced by two-thirds for 10 years, stockpile reduced from ~10,000 kg to 300 kg LEU, Arak reactor redesigned to prevent plutonium production, IAEA Additional Protocol implemented. In exchange: UN, EU, and US sanctions lifted. The JCPOA was implemented on 16 January 2016 (Implementation Day) after IAEA verification.

Phase 5: US Withdrawal, Escalation, and Conflict (2018–2026)

On 8 May 2018, the US withdrew from the JCPOA and reimposed sanctions under a "maximum pressure" campaign. From July 2019, Iran began systematically breaching JCPOA limits: exceeding LEU stockpile caps, enriching beyond 3.67%, installing advanced centrifuges. By February 2023, uranium enriched to 83.7% purity was detected at Fordow. JCPOA revival talks (JCPOA-2 negotiations) in Vienna collapsed repeatedly. The E3 (France, Germany, UK) triggered the UNSC snapback mechanism on 28 August 2025, reimposing all pre-JCPOA UN sanctions on 27 September 2025. On 28 February 2026, the US and Israel launched coordinated military strikes on Iran's nuclear facilities (including Natanz and Fordow). Iran retaliated, triggering a broader West Asia conflict. The Islamabad MoU of 17 June 2026 established a ceasefire and 60-day negotiation window.

UNSC Snapback Mechanism (Resolution 2231)

UNSC Resolution 2231 (adopted 20 July 2015) endorsed the JCPOA and created a snapback mechanism: any JCPOA participant-state could notify the Security Council of "significant non-performance" by Iran, automatically triggering the reimposition of all pre-JCPOA UN sanctions within 30 days — without a veto being applicable. The E3 invoked this on 28 August 2025; China, Russia, and Iran disputed the legal standing of the invocation, but the sanctions were technically reimposed on 27 September 2025. This was a significant escalatory step that preceded the February 2026 military strikes.

Key Facts & Data

• Iran signed NPT: July 1968 (ratified February 1970)
• Tehran Research Reactor: operational 1967, US-supplied
• Natanz enrichment facility and Arak heavy water plant: secretly constructed; disclosed August 2002
• A.Q. Khan network supplied centrifuge designs to Iran from the 1980s
• JCPOA signed: 14 July 2015 (Vienna); implemented 16 January 2016
• JCPOA enrichment cap: 3.67%; LEU stockpile ceiling: 300 kg
• US JCPOA withdrawal: 8 May 2018
• Iran's peak enrichment: 83.7% U-235 (Fordow, February 2023)
• Pre-war stockpile at 60%: ~440.9 kg (May 2025 IAEA estimate)
• UNSC snapback invoked: 28 August 2025; sanctions reimposed 27 September 2025
• Islamabad MoU signed: 17 June 2026; 60-day negotiation clock started