August 2002: Western intelligence services and an Iranian opposition group reveal a covert nuclear site at the central city of Natanz. An inspection by the UN’s International Atomic Energy Agency reveals it was used to enrich uranium, a process for producing fuel or nuclear warheads.

June 2003: Britain, France and Germany engage Iran in nuclear negotiations. Washington refuses to join.

October 2003: Iran suspends uranium enrichment.

February 2006: Iran announces it will restart uranium enrichment following the election of hard-line President Mahmoud Ahmadinejad.

June 2006: The United States, Russia and China join Britain, France and Germany to form the P5+1 group of nations trying to persuade Iran to curb its nuclear program.

December 2006: The UN Security Council imposes the first set of sanctions on Iran, banning the sale of sensitive nuclear technology. More follow as time goes on.

November 2007: The number of uranium-enriching centrifuges assembled by Iran reaches about 3,000 from just a few hundred in 2002. Its stockpile of low-enriched uranium also grows.

July 2008: Under President George W. Bush, the United States joins the nuclear talks for the first time.

October 2009: Under President Barack Obama, a senior US diplomat meets one-on-one with Iran’s top nuclear negotiator.

February 2010: Iran announces it has started to enrich uranium to near 20 per cent, a technical step away from weapons-grade material.

November 2011: The IAEA outlines the possible military dimension to Iran’s nuclear activities. Iran denies the allegations, saying they’re based on falsified Israeli and US evidence.

April 2012: Negotiations restart between Iran and world powers.

July 2012: US and Iranian officials meet secretly in Oman to see if diplomatic progress is possible. Talks gain speed the following year, particularly when Ahmadinejad’s presidency ends.

August 2013: Hassan Rouhani, a relatively moderate cleric, defeats several hard-line candidates to become Iran’s president.

-September 2013: Rouhani and Obama speak by telephone, the highest-level exchange between the two countries since Iran’s 1979 Islamic Revolution.

November 2013: Iran and the six powers announce an interim agreement that temporarily curbs Tehran’s nuclear program and unfreezes some Iranian assets.

June 16, 2015: New York businessman Donald Trump announces he’s running for president and says of the yet-finalised Iran deal: “It’s a disaster.”

July 14, 2015: World powers and Iran announce long-term, comprehensive nuclear agreement.

October 2015: Iran conducts its first ballistic missile test since the nuclear deal. The US accuses Iran of violating a UN Security Council resolution, but the Obama acknowledges that ballistic missiles are “entirely separate” from the nuclear deal. Iran continues its tests, saying its missiles serve as a defensive deterrent in a region heavily armed by the US.

Jan. 17, 2016: The US imposes new sanctions over Iran’s ballistic missile tests.

Nov. 9, 2016: Trump wins US presidential election.

May 19, 2017: Rouhani is re-elected as Iran’s president.

Oct. 13, 2017: Trump announces he will not re-certify the Iran nuclear deal as required, criticising the accord by saying it “threw Iran’s dictatorship a political and economic lifeline.”

November 2017: The US, Western nations and the UN say Iran has been supplying Shiite rebels in Yemen with the ballistic missiles used to target Saudi Arabia’ capital, Riyadh. Tehran denies it.

Jan. 12: Trump administration re-issues waivers on nuclear deal sanctions, but warns Trump will withdraw from the deal if Congress does not address his concerns. Trump administration also says it wants a supplemental deal on Iran with European allies.

May 8: Trump says he’ll announce his decision on whether to pull the US from the nuclear deal.