TIMELINE: Iran's nuclear program

(Reuters) - Six world powers agreed on Friday to push ahead with a third round of tougher sanctions against Iran unless reports later this month indicate Tehran has tried to address their concerns about its nuclear program.

Here is a chronology since it emerged that Iran was carrying out sensitive work that it could use to make atomic bombs. Tehran insists its activities are peaceful:

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

December 2002 - The 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.

September 2, 2005 - IAEA report confirms Iran has resumed uranium conversion at Isfahan.

January 10, 2006 - Iran removes U.N. seals at Natanz enrichment plant and resumes nuclear fuel research.

February 4 - IAEA votes to report Iran to the U.N. Security Council. Iran ends snap U.N. nuclear inspections the next day.

February 14 - Iran restarts small-scale feeding of uranium gas into centrifuges at Natanz after 2-1/2-year suspension.

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

June 5 - EU foreign policy chief Javier Solana delivers a package of incentives from world powers if Iran agrees to halt uranium enrichment.

July 31 - The U.N. Security Council demands that Iran suspend its nuclear activities by August 31.

August 31 - IAEA announces Iran has not met deadline to suspend its atomic fuel program.

December 23 - Security Council votes for sanctions and gives 60 days to suspend enrichment. Iran calls the resolution illegal.

March 24 - The Security Council unanimously approves new arms and financial sanctions against Iran.

April 18 - IAEA says Iran has begun making nuclear fuel in its underground uranium enrichment plant.

May 23 - A confidential IAEA report says Iran has not suspended enrichment-related work.

Aug 21 - Iran and the IAEA say they agreed a timeline for answering outstanding questions about Iran's nuclear program.

Oct 4 - Diplomats say Iran has installed close to 3,000 centrifuge machines, enough to start refining usable amounts of nuclear fuel if they worked without glitches.

Oct 20 - Saeed Jalili is named to replace chief nuclear negotiator Ali Larijani, who resigned.

Oct 24 - The U.S. imposes new sanctions on Iran and accuses Revolutionary Guard of spreading weapons of mass destruction.

Nov 2 - Britain, France, Germany, the U.S., Russia and China agree to push ahead with a third round of tougher sanctions. The six say they will meet again on November 19 to assess reports from IAEA head Mohamed ElBaradei.