TIMELINE: Iran's nuclear program

(Reuters) - Iran has told the U.N. nuclear watchdog it is building a second uranium enrichment plant, a belated revelation likely to worsen Tehran's confrontation with Western powers over suspicions it is seeking nuclear weapons capability.

Details of Iran's nuclear program emerged in August 2002 when the exiled opposition National Council of Resistance of Iran reported the existence of a uranium enrichment facility at Natanz and a heavy water plant at Arak.

Here is a timeline of Iran and its nuclear program in the last two years:

November 2, 2007 - Britain, France, Germany, the United States, Russia and China agree to push ahead with more sanctions after Iran refuses to suspend uranium enrichment.

December 3 - A U.S. National Intelligence Estimate says Iran put its program to build a nuclear bomb on hold in 2003.

December 11 - The opposition NCRI says Iran did shut down its program in 2003 but restarted it a year later. The group says the U.S. analysis gives the wrong impression.

March 3, 2008 - U.N. Security Council adopts a third sanctions resolution targeted at Iran's nuclear program.

July 19 - Iranian officials rule out any freeze in uranium enrichment during talks in Geneva on the program, attended for the first time by a senior U.S. diplomat.

August 2 - An informal deadline lapses for Iran to respond to an offer from the United States, Britain, France, Germany, China and Russia for talks.

August 5 - Iran sends a letter to the powers but gives no concrete reply to a demand to freeze its nuclear activity, a step the United States says amounts to obfuscation. Washington and London say the powers may consider more U.N. sanctions.

September 15 - The IAEA says Iran has blocked a U.N. inquiry into whether it researched ways to develop a nuclear bomb.

February 5, 2009 - Russia says it plans to start up a nuclear reactor at the Bushehr plant by the end of 2009.

February 19 - An IAEA report shows a significant increase in Iran's stockpile of low-enriched uranium; enough, physicists say, for conversion into highly enriched uranium for one bomb.

March 20 - After years of U.S. attempts to isolate Iran, new President Barack Obama calls for "engagement that is honest and grounded in mutual respect." Iran cautiously welcomes the overture, but said it wanted to see "practical steps."

April 9 - Iranian President Mahmoud Ahmadinejad says Iran has mastered the nuclear fuel cycle and also tested further advanced machines for enriching uranium. He also inaugurates the nation's first atomic fuel fabrication plant near Isfahan.

June 5 - A quarterly IAEA report says Iran now has 7,231 centrifuge enrichment machines installed, a 25 percent increase in potential capacity since March.

June 12 - Ahmadinejad re-elected president. Protests break out by moderates who say the result was fixed.

August 21 - Diplomats say Iran has allowed IAEA officials to inspect the Arak heavy-water site as well as an upgrade to IAEA monitoring at the Natanz uranium enrichment plant.

August 25 - Diplomats say there has been no increase in the number of centrifuges enriching uranium since the end of May.

August 28 - The IAEA reports Iran has slightly reduced the scale of its uranium enrichment. But it has also raised the number of installed centrifuge machines by some 1,000 to 8,308.

September 1 - Iran says it has prepared an updated nuclear proposal and is ready to resume talks with world powers.

September 2 - Mohamed ElBaradei, outgoing director-general of the IAEA says Iran is not going to produce a nuclear weapon any time soon and the threat cited has been exaggerated.

September 7 - Ahmadinejad says Iran will continue its disputed nuclear work and will never negotiate on its "obvious" rights.

September 9 - Iran hands over a package of proposals which it says addresses "various global issues" and represents a "new opportunity for talks and cooperation."

September 12 - Foreign Minister Manouchehr Mottaki says Iran will not back down in its nuclear row with the West, a day after the United States said it would accept Tehran's offer of wide-ranging talks with six world powers.

September 14 - Iranian news agencies and the European Union say Iran and world powers will start talks on October 1.

September 17 - Ahmadinejad says Iran would "never" abandon its nuclear program to appease Western critics.

September 24 - China dampens expectations of further sanctions on Iran, telling other major powers that more pressure would not persuade Tehran to halt its nuclear program.

-- In contrast, British Prime Minister Gordon Brown tells the U.N. Security Council the world should consider "far tougher sanctions" if Iran continues to seek a nuclear weapon.

September 25 - The IAEA says Iran has told it about a second uranium enrichment plant under construction.

(Writing by David Cutler, London Editorial Reference Unit; Additional writing by Jijo Jacob);