US–Iran nuclear timeline: Decades of tension explained

The United States and Iran have reached an interim deal aimed at ending the war and reopening the Strait of Hormuz.

There are plans for a signing of the deal on Friday in Switzerland. However, previous announcements fell through, and what the deal contained remained in dispute Monday.

Here's a timeline of the tensions over Iran's atomic program:

1967 - Iran takes possession of the Tehran Research Reactor supplied by America under the "Atoms for Peace" program.

1979 - US ally Shah Mohammad Reza Pahlavi, fatally ill, flees Iran as popular protests against him surge. Ayatollah Ruhollah Khomeini returns to Tehran and the Islamic Revolution sweeps him to power. Students seize the US Embassy in Tehran, beginning the 444-day hostage crisis. Iran's nuclear program goes fallow under international pressure.

August 2002 - Western intelligence services and an Iranian opposition group reveal Iran's secret Natanz nuclear enrichment facility.

June 2003 - Britain, France and Germany engage Iran in nuclear negotiations.

October 2003 - Iran suspends uranium enrichment under international pressure.

February 2006 - Iran announces it will restart uranium enrichment following the election of hard-line President Mahmoud Ahmadinejad. Britain, France and Germany walk out of stalled negotiations.

June 2009 - Iran's disputed presidential election sees Ahmadinejad reelected despite fraud allegations, sparking protests known as the Green Movement and a violent government crackdown.

October 2009 - Under US President Barack Obama, the US and Iran open a secret back-channel for messages in the sultanate of Oman.

July 2012 - US and Iranian officials hold secret face-to-face talks in Oman.

July 2015 - World powers and Iran announce a long-term, comprehensive nuclear agreement that limits Tehran's enrichment of uranium in exchange for the lifting of economic sanctions.

May 8, 2018 - US President Donald Trump unilaterally withdraws the US from the nuclear agreement, calling it the "worst deal ever." He says he'll get better terms in new negotiations to stop Iran's missile development and support for regional militias. Those talks don't happen in his first term.

May 8, 2019 - Iran announces it will begin backing away from the accord. A series of regional attacks on land and at sea blamed on Tehran follow.

Jan. 3, 2020 - A US drone strike in Baghdad kills Gen. Qassem Soleimani, the architect of Tehran's proxy wars in the Middle East.

Jan. 8, 2020 - In retaliation for Soleimani's killing, Iran launches a barrage of missiles at military bases in Iraq that are home to thousands of American and Iraqi troops. More than 100 US service members suffer traumatic brain injuries, according to the Pentagon. As Iran braces for a counterattack, the Revolutionary Guard shoots down a Ukrainian passenger plane shortly after takeoff from Tehran's international airport, reportedly mistaking it for a US cruise missile. All 176 people on board are killed.

July 2, 2020 - A mysterious explosion tears apart a centrifuge production plant at Iran's Natanz nuclear enrichment facility. Iran blames the attack on Israel.

April 6, 2021 - Iran and the US under President Joe Biden begin indirect negotiations in Vienna over how to restore the nuclear deal. Those talks, and others between Tehran and European nations, fail to reach any agreement.

April 11, 2021 - A second attack within a year targets Iran's Natanz nuclear site, again likely carried out by Israel.

April 16, 2021 - Iran begins enriching uranium up to 60% - its highest purity ever and a technical step from weapons-grade levels of 90%.

Feb. 24, 2022 - Russia launches its full-scale invasion of Ukraine. Moscow ultimately will come to rely on Iranian bomb-carrying drones in the conflict, as well as missiles.

July 17, 2022 - An adviser to Iran's supreme leader, Kamal Kharrazi, says Iran is technically capable of making a nuclear bomb, but has not decided whether to build one.

Oct. 7, 2023 - Hamas militants from the Gaza Strip storm into Israel, killing around 1,200 people and taking 251 others hostage, beginning the most intense war ever between Israel and Hamas. Iran, which has armed Hamas, offers support to the militants. Regional tensions spike.

Nov. 19, 2023 - Yemen's Houthi rebels, long supported by Iran, seize the ship Galaxy Leader, beginning a monthslong campaign of attacks on shipping through the Red Sea corridor that the US Navy describes as the most intense combat it has seen since World War II. The attacks mirror tactics earlier used by Iran.

April 14, 2024 - Iran launches an unprecedented direct attack on Israel, firing over 300 missiles and attack drones. Israel, working with a US-led international coalition, intercepts much of the incoming fire.

April 19, 2024 - A suspected Israeli strike hits an air defense system by an airport in Isfahan, Iran.

July 31, 2024 - Ismail Haniyeh, a Hamas leader, is assassinated during a visit to Tehran after the inauguration of reformist President Masoud Pezeshkian. Israel later takes responsibility for the assassination.

Sept. 27, 2024 - An Israeli airstrike kills Hezbollah leader Hassan Nasrallah in Lebanon.

Oct. 1, 2024 - Iran launches its second direct attack on Israel, though a US-led coalition and Israel shoot down most of the missiles.

Oct. 16, 2024 - Israel kills Hamas leader Yahya Sinwar in the Gaza Strip.

Oct. 26, 2024 - Israel openly attacks Iran for the first time, striking air defense systems and sites associated with its missile program.

Jan. 20, 2025 - Trump is inaugurated for his second term as president.

Feb. 7, 2025 - Iran's Supreme Leader Ayatollah Ali Khamenei says proposed talks with the US are "not intelligent, wise or honorable."

March 7, 2025 - Trump says he sent a letter to Khamenei seeking a new nuclear deal with Tehran.

March 15, 2025 - Trump launches intense airstrikes targeting Houthi rebels in Yemen, the last members of Iran's self-described "Axis of Resistance" capable of daily attacks.

April 7, 2025 - Trump announces the US and Iran will hold direct talks in Oman. Iran says they'll be indirect talks.

April 12, 2025 - The first round of talks between Iran and the US take place in Oman, ending with a promise to hold more talks after US Mideast envoy Steve Witkoff and Iranian Foreign Minister Abbas Araghchi "briefly spoke" together.

April 19, 2025 - The second round of talks between the US and Iran are held in Rome.

April 26, 2025 - Iran and the US meet in Oman a third time, but the negotiations include talks at the expert level for the first time.

May 11, 2025 - Iran and the US meet in Oman for a fourth round of negotiations ahead of Trump's trip to the Mideast.

May 23, 2025 - Iran and the US meet in Rome for a fifth round of talks, with Oman saying the negotiations made "some but not conclusive progress."

June 9, 2025 - Iran signals it won't accept a US proposal over the nuclear program.

June 12, 2025 - The Board of Governors at the International Atomic Energy Agency finds Iran in noncompliance with its nuclear obligations. Iran responds by announcing it has built and will activate a third nuclear enrichment facility.

June 13, 2025 - Israel launches its war against Iran. Over 12 days, it hits nuclear and military sites, as well as other government installations.

June 22, 2025 - The US intervenes in the war, attacking three Iranian nuclear sites.

June 23, 2025 - Iran responds to the US attack by targeting a military base in Qatar used by American troops, causing limited damage.

June 24, 2025 - Trump announces a ceasefire in the war.

July 25, 2025 - Iranian and European diplomats hold talks in Istanbul over Iran's nuclear program.

Aug. 8, 2025 - France, Germany and the United Kingdom warn Iran in a letter that it will reimplement U.N. sanctions if there is no "satisfactory solution" to the nuclear standoff by Aug. 31.

Aug. 28, 2025 - France, Germany and the United Kingdom say they've started the process to "snapback" U.N. sanctions on Iran.

Sept. 9, 2025 - Iran and the International Atomic Energy Agency reach a deal over potentially starting inspections, but questions remain over its implementation.

Sept. 19, 2025 - U.N. Security Council declines to stop "snapback" sanctions on Iran.

Sept. 26, 2025 - U.N. Security Council rejects China and Russia's last-minute effort to stop "snapback."

Sept. 28, 2025 - U.N. reimposes "snapback" sanctions on Iran barring any last-minute diplomacy.

Dec. 28, 2025: Protests break out in two major markets in downtown Tehran after the Iranian rial plunges to a record low - 1.42 million rials to one US dollar - compounding inflationary pressure and pushing up the prices of food and other daily necessities.

Jan. 3, 2026: Khamenei says "rioters must be put in their place," in what is seen as a green light for security forces to begin more aggressively putting down the demonstrations.

Jan. 8, 2026: Following a call from Iran's exiled crown prince, a mass of people shout from their windows and take to the streets in nationwide protests. The government responds by blocking the internet and international telephone calls to cut off the country from outside influence. An ensuing security force crackdown kills thousands and sees tens of thousands detained.

Jan. 13, 2026: Trump says he has called off any meetings with the Iranians and promises that unspecified "help is on its way."

Jan. 26, 2026: The aircraft carrier USS Abraham Lincoln and three accompanying warships arrive in the Middle East amid Trump's threats to attack.

Feb. 3, 2026: A US Navy fighter jet shoots down an Iranian drone approaching the Lincoln in the Arabian Sea. Iranian fast-attack boats attempt to stop a US-flagged ship in the Strait of Hormuz.

Feb. 6, 2026: Iran and the US hold indirect nuclear talks in Oman, with the head of the US military's Central Command also coming.

Feb. 17, 2026: Iran and the US hold talks in Geneva while Tehran says it has temporarily closed the Strait of Hormuz, the narrow mouth of the Persian Gulf through which a fifth of all oil traded passes.

Feb. 26, 2026: Iran and the US hold another round of talks in Geneva as America assembles the largest fleet of warplanes and aircraft in the Mideast in decades.

Feb. 28, 2026: Israel and the United States launch a war on Iran, killing Khamenei in the conflict's first moments.

March 9, 2026: Iran names Ayatollah Mojtaba Khamenei, the late supreme leader's son, as country's new paramount ruler.

April 7, 2026: A fragile ceasefire in the Iran war is announced, with talks to continue. Israel is not included in negotiations.

April 8, 2026: Israel bombards Lebanon's capital, Beirut, killing over 300 people in a 10-minute attack.

April 11, 2026: US Vice President JD Vance leads an American delegation to Islamabad, meeting with Iranian team led by parliament speaker Mohammad Bagher Qalibaf, the highest-level direct talks between the two nations since the 1979 Islamic Revolution. The talks end after 21 hours without a deal.

May 31, 2026: Israel's ground invasion of Lebanon makes its deepest incursion in over a quarter century.

June 15, 2026: The United States and Iran reach an initial agreement to open the Strait of Hormuz and further extend a shaky ceasefire in the Iran war.