Iran and the U.S. will hold talks on Saturday on Iran's nuclear programme, with U.S. President Donald Trump having threatened military action if they cannot agree a deal.
Iran's nuclear programme has been the subject of a long dispute between it and Western countries that fear it wants to build an atomic bomb, which Tehran denies.
Here is a timeline of the dispute:
1957 - Iran and United States sign a nuclear cooperation deal and the United States delivers a research reactor to Iran a decade later.
1970 - Iran ratifies the Nuclear Nonproliferation Treaty (NPT), giving it the right to a civilian nuclear programme but barring it from seeking an atomic bomb.
1979 - Iran's Islamic revolution upends its ties to major powers, turning former ally the United States into its main foe.
1995 - Russia agrees to finish construction of Iran's planned nuclear power plant at Bushehr, originally started by Germany and shelved since the revolution.
2003 - The U.N. nuclear watchdog, the International Atomic Energy Agency, says Iran has not complied with NPT after the revelation it has secretly built a uranium enrichment plant at Natanz and a heavy water plant for plutonium at Arak.
Both can be used to make fuel for nuclear power but they can also be used in atomic warheads.
Iran accepts European proposals for more transparency in its nuclear programme including snap IAEA inspections.
2004 - The IAEA says Iran has not provided the transparency it promised. Iran says it will not suspend uranium enrichment activity.
2005 - Russia offers to supply Iran with fuel for Bushehr to stop it developing its own fuel by making enriched uranium or plutonium.
IAEA says Iran is not in compliance with agreements and EU countries halt negotiations.
2006 - Iran resumes work at Natanz, saying in April it has enriched uranium for the first time to about 3.5%, far short of the 90% needed for a warhead.
World powers the U.S., Russia, China, France, Britain and Germany - later known collectively as the P5+1 - offer Iran incentives to halt enrichment.
The United Nations Security Council imposes sanctions on Iran over its enrichment.
2009 - Western countries say Iran has been building another secret uranium enrichment facility under a mountain at Fordow near Qom.
2010 - Iran starts making 20% enriched uranium. The U.N. Security Council expands sanctions including an embargo on major weapons systems, as the U.S. and EU tighten their own sanctions.
A computer virus - Stuxnet - appears aimed at paralysing the Natanz plant, the start of direct operations against Iranian facilities that Tehran blames on Israel.
2011 - Bushehr nuclear plant starts operations. Iran says it will use more advanced centrifuges to expand its 20% enrichment programme.
2013 - Former nuclear negotiator Hassan Rouhani is elected Iranian president offering new proposals. He and U.S. President Barack Obama hold a first call between leaders of the countries since 1979.
Iran-P5+1 talks in Geneva result in a "Joint Plan of Action" with steps required by both sides including reducing Iran's enriched uranium stockpile, more IAEA access and some sanctions relief.
2014 - Negotiations on a final deal continue through the year, with Iran halting uranium enrichment to 20% and work at Arak and getting access to oil revenue frozen by sanctions.
U.S. allies in the region, Israel and Saudi Arabia, repeatedly caution Washington against a deal, saying Iran cannot be trusted and citing its growing sway in the region.
2015 - Iran and the P5+1 agree the Joint Comprehensive Plan of Action (JCPOA) deal that limits Iran's nuclear work, allows for more inspections and a loosening of sanctions.
2016 - IAEA says Iran has met its commitments under the JCPOA, leading to UN sanctions tied to the nuclear programme being lifted.
However, Iran's long-range ballistic missile tests prompt unease despite Tehran saying they could not carry nuclear warheads.
2017 - New U.S. President Donald Trump says the JCPOA is the "worst deal ever" and unilaterally pulls out. Despite Trump promising a better deal there are no new talks.
2018 - The United States resumes sanctions on Iran, which starts to move away from the JCPOA.
2019 - With ties between Iran and the West deteriorating, a string of attacks on Gulf oil tankers and other regional energy facilities are blamed by the U.S. on Iran.
2020 - A blast rocks Iran's Natanz plant and a nuclear scientist is assassinated near Tehran with Iran blaming both incidents on Israel.
2021 - With Trump out of the White House, U.S. and Iran resume indirect talks but there is little progress.
Iran starts enriching uranium to 60% - not far from 90% needed for a bomb.
New attacks strike Iran's Natanz and a centrifuge factory in Karaj.
2022 - The IAEA says Iran did not answer questions over uranium traces found at more sites. Iran cuts off IAEA inspections and installs more new centrifuges at Natanz.
2025 - Trump returns to the White House and says Iran must agree to a nuclear deal or "there will be bombing".
