Long, fraught timeline of tensions between Iran and the US

Iran and the United States held a fifth round of talks in Rome on Friday over Tehran's rapidly advancing nuclear program.

The negotiations represent a milestone in the fraught relations between the two nations over Iran's program, which is enriching uranium close to weapons-grade levels. Officials are now focused on the details that could make or break any accord.

Here's a timeline of the tensions between the two countries over Iran's atomic program.

Early days

1967 — Iran takes possession of its Tehran Research Reactor under America's ''Atoms for Peace'' program.

1979 — 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 United States 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.

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 re-elected despite fraud allegations, sparking Green Movement protests and violent government crackdown.

October 2009 — Under President Barack Obama, the U.S. and Iran open a secret backchannel for messages in the sultanate of Oman.

July 2012 — U.S. and Iranian officials hold face-to-face secret talks in Oman.

July 14, 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.

The nuclear deal collapses

May 2018 — Trump unilaterally withdraws the U.S. 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 U.S. 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 U.S. service members suffer traumatic brain injuries. 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 U.S. cruise missile. All 176 people on board are killed.

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

April 6, 2021 — Iran and the U.S. 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 that Iran is technically capable of making a nuclear bomb, but has not decided whether to build one. His remarks will be repeated by others in the coming years as tensions grow.

Mideast wars rage

Oct. 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 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 U.S. 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 U.S.-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 apparently by Israel during a visit to Tehran after the inauguration of reformist President Masoud Pezeshkian.

Sept. 27, 2024 — Israeli airstrike kills Hezbollah leader Hassan Nasrallah.

Oct. 1, 2024 — Iran launches its second direct attack on Israel, though a U.S.-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.

Trump returns — and reaches out

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 U.S. 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 U.S. and Iran will hold direct talks in Oman. Iran says they'll be indirect talks, but confirms the meeting.

April 12, 2025 — First round of talks between Iran and the U.S. take place in Oman, ending with a promise to hold more talks after U.S. Mideast envoy Steve Witkoff and Iranian Foreign Minister Abbas Araghchi ''briefly spoke'' together.

April 19, 2025 — Second round of talks between the U.S. and Iran are held in Rome.

April 26, 2025 — Iran and the U.S. 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 U.S. meet in Oman for a fourth round of negotiations ahead of Trump's trip to the Mideast.

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