The United Nations Security Council voted unanimously Saturday to impose sanctions on Iran's trade in sensitive nuclear materials and ballistic missiles, a move aimed at getting Tehran to halt uranium enrichment work.

Here are the main events since Iran's nuclear program, which it says is purely peaceful, first came to light:

August 2002: Exiled opposition National Council of Resistance of Iran reports the existence of uranium enrichment facility at Natanz and heavy water plant at Arak.

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December 2002: United States accuses Iran of "across-the-board pursuit of weapons of mass destruction."

June 2003: International Atomic Energy Agency (IAEA) report, after February inspection of Natanz and Arak, says Iran has failed to comply with nuclear Non-Proliferation Treaty.

December 2003: Iran signs protocol allowing snap inspections of nuclear facilities.

November 2004: Iran promises EU negotiators it will suspend all nuclear fuel processing and reprocessing work.

February 2005: Iranian President Mohammad Khatami says no Iranian government will give up nuclear technology program.

September 2, 2006: IAEA report confirms Iran has resumed uranium conversion at Isfahan.

January 10, 2006: Iran removes UN seals at Natanz enrichment plant and resumes nuclear fuel research.

February 4, 2006: IAEA votes to report Iran to UN Security Council.

February 5, 2006: Iran ends snap UN nuclear inspections.

February 14, 2006: Iran restarts small-scale feeding of uranium gas into centrifuges at Natanz after two-and-a-half-year suspension.

March 8, 2006: IAEA report to Security Council says it cannot verify Iran's atomic activities are peaceful.

April 11, 2006: Iran announces it has produced low-grade enriched uranium suitable for use in power stations; IAEA confirms this.

April 28, 2006: An IAEA report, sent to the Security Council, confirms Iran has flouted council demands to suspend enrichment.

June 5, 2006: European Union foreign policy chief Javier Solana visits Tehran to deliver a package of incentives from world powers if Iran agrees to halt uranium enrichment.

July 31, 2006: Security Council demands Iran suspend its nuclear activities by August 31. In a resolution, council for first time makes legally binding demands on Iran and threat of sanctions. Iran's ambassador to the UN rejects the resolution.

August 26, 2006: Iran launches new phase in Arak heavy-water reactor project.

August 31, 2006: IAEA announces Iran has not met deadline to suspend its atomic fuel program and has resumed enriching small amounts of uranium in recent days.

September 19, 2006: U.S. President Bush and Iranian President Ahmadinejad clash over Iran's nuclear ambitions at the United Nations.

September 26, 2006: Russia and Iran agree start-up date of September 2007 for Iran's first nuclear power station at Bushehr, with power sent to grid in November 2007.

October 6, 2006: Six world powers say they have agreed to discuss sanctions to punish Tehran for failing to halt uranium enrichment but are still open to negotiations.

November 14, 2006: A confidential IAEA report says Iran is pushing ahead with uranium enrichment and still stonewalling investigations by the agency despite the risk of sanctions.

The report also says Iran has started up second experimental chain of 164 interlinked centrifuge machines and has begun feeding uranium UF6 gas into them for enrichment.

December 23, 2006: Security Council votes to impose sanctions. Iran calls the resolution an illegal measure.