The US and Iran are preparing for high-level talks in Oman on Saturday. The negotiations are a revival of efforts to prevent Iran from developing a nuclear weapons programme, which it denies seeking, in exchange for easing of sanctions that have taken a heavy toll on its economy.
A 2015 deal between Tehran and six world powers – the US, Russia, China, France, the UK and Germany – came to nothing after President Donald Trump abandoned the deal in 2018.
2013 - 2019: Deal made, then broken
November 2013: Iran and the six powers announce an interim agreement that temporarily curbs Tehran's nuclear programme and unfreezes some Iranian assets, setting the stage for negotiations on a comprehensive nuclear accord.
April 2015: A framework nuclear deal is announced, outlining long-term restrictions on Iran’s nuclear programme and the removal of many international sanctions.
July 14, 2015: World powers and Iran announce a long-term, comprehensive nuclear agreement.
May 2018: Mr Trump, in the second year of his first term, unilaterally withdraws the US from the nuclear agreement, calling it the “worst deal ever”.
August 2018: The Trump administration begins to reimpose sanctions on Iran that were lifted under the nuclear accord, targeting a range of sectors from carpets and pistachios to gold and commercial aircraft. This is part of the "maximum pressure" strategy.
November 2018: The US re-enforces the most onerous sanctions that were lifted under the deal, targeting Iran’s banking and oil sectors.
April 2019: Mr Trump designates Iran’s Islamic Revolutionary Guard Corps as a foreign terrorist organisation, the first time the US has blacklisted part of another nation’s military in this way.
May 2019: Iran announces it will begin breaching the accord, setting a 60-day ultimatum for Europe to compensate for American-led sanctions before it begins enriching uranium to higher levels.
June 25, 2019: Mr Trump imposes new sanctions on supreme leader Ali Khamenei and his associates.
July 1, 2019: Iran announces it has exceeded the nuclear deal’s curbs on its low-enriched uranium stockpile.
September 3, 2019: The US sanctions Iran’s civilian space agency, alleging the programme is cover for testing ballistic missile technology.
September 7, 2019: Iran begins spinning advanced gas enrichment centrifuges prohibited under the 2015 deal.
November 6, 2019: Iran injects uranium gas into centrifuges at its underground Fordow plant.
2020: Suspected sabotage and a new US president
April 22, 2020: The IRGC launches its first satellite into space, revealing what experts describe as a secret military space programme.
July 2020: An explosion at a centrifuge production plant at Iran’s Natanz nuclear enrichment facility. Iran blames the blast on Israeli sabotage.
October 2020: A decade-long UN arms embargo on Iran that banned it from purchasing foreign weapons expires as scheduled under the nuclear deal, despite American objections.
November 2020: Joe Biden wins the US presidential election.
2021: IAEA oversight weakened
January 4, 2021: Iran begins enriching uranium up to 20 per cent and seizes a South Korean-flagged oil tanker near the Strait of Hormuz.
February 23, 2021: The International Atomic Energy Agency loses access to its surveillance cameras, as well as data from its online enrichment monitors and electronic seals amid a standoff with Iran. Tehran pledges to hold on to the tapes and give them back when granted sanctions relief.
April 6, 2021: Iran and the US begin indirect negotiations in Vienna over how to restore the nuclear deal.
April 11, 2021: A second attack on the Natanz nuclear site, with suspicion again falling on Israel.
April 16, 2021: Iran begins enriching uranium up to 60 per cent – its highest purity so far and a technical step from weapons-grade levels of 90 per cent.
June 19, 2021: Ebrahim Raisi, a hardline protege of Mr Khamenei, is elected Iran's president.
December 1, 2021: The IAEA says Iran has begun feeding 166 advanced IR-6 enrichment centrifuges at Fordow.
December 15, 2021: The IAEA and Iran reach a deal to reinstall cameras damaged at the Karaj nuclear facility, although inspectors' access to video is restricted.
2022: Opportunities lost
March 12, 2022: Nuclear talks in Vienna break off without an agreement as Russia demands guarantees that its ties with Tehran be exempted from western sanctions over its war in Ukraine.
May 11, 2022: The European Union sends its envoy for the nuclear talks to Tehran, as negotiations hit a deadlock over Iran’s demand that Washington lift its terrorism designation of the IRGC.
June 8, 2022: IAEA board of governors censures Iran for failing to provide answers on man-made traces of uranium found at three undeclared sites. Iran disconnects two IAEA surveillance cameras.
June 9, 2022: Iran begins disconnecting 27 IAEA surveillance cameras at the country’s nuclear sites, as it prepares to install more IR-6 centrifuges at Natanz.
June 28, 2022: Iran and the US begin a series of indirect talks in Qatar over the nuclear deal.
August 4, 2022: Negotiators from Iran, the US and the EU hold indirect talks on a tentative deal, but it falls apart. France, Germany and Britain later say Iran “has chosen not to seize this critical diplomatic opportunity”.
November 17, 2022: The IAEA censures Iran for failing to co-operate with its safeguards investigation.
2023: Iran's proxies spark rise in regional tensions
February 23, 2023: Iran directly acknowledges an accusation attributed to international inspectors that it enriched particles of uranium to 84 per cent purity for the first time. The issue ultimately is settled, but puts new pressure on negotiators.
October 7, 2023: Hamas militants from the Gaza Strip storm into Israel, killing 1,200 people and taking 250 others hostage. This begins the most-intense war yet between Israel and Hamas. Iran, which has armed Hamas, offers support to the militants. Regional tensions spike.
2024 - 2025: Return of Trump
June 5, 2024: The IAEA board of governors censures Iran for failing to co-operate fully with the agency.
June 14, 2024: The IAEA says Iran has started up new cascades of advanced centrifuges and plans to install others after facing criticism over its nuclear programme.
November 2024: Mr Trump wins the US presidential election.
April 7, 2025: Mr Trump makes a surprise announcement that the US and Iran will begin talks on Tehran's nuclear programme.
April 9, 2025: Iran welcomes US investors and offers nuclear assurances in major shift of tone.
