REUTERS - President Mahmoud Ahmadinejad said on Tuesday Iran was ready to send its enriched uranium abroad in exchange for nuclear fuel, a move which could break an impasse over its disputed nuclear programme.

Following are key moments in negotiations with Iran on its nuclear programme:

IRAN-EU3 TALKS

October 2003 - After the U.N. nuclear watchdog says Iran hid its nuclear enrichment programme from U.N. inspectors for nearly two decades, Iran agrees to negotiate with Britain, France and Germany on a package of economic and political incentives and promises to suspend its uranium enrichment programme. European officials involved in the "EU3" talks with Iran say they are aimed at reaching a peaceful agreement with the Iranians that would avoid military action.

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U.S. officials are sceptical and say the talks are doomed to fail. The vast majority of members of the governing board of the U.N. nuclear watchdog in Vienna, the International Atomic Energy (IAEA), agree not to refer Iran's nuclear programme to the U.N. Security Council for possible sanctions while negotiations between Tehran and the EU3 are underway.

SECURITY COUNCIL REFERRAL

February 2006 - After 2-1/2 years of fitful talks, the European trio break off negotiations with Iran in January 2006. The following month Iran begins enriching uranium and the IAEA board of governors votes to refer Iran's nuclear programme to the U.N. Security Council.

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IAEA chief Mohamed ElBaradei makes clear he opposes sending the Iran issue to the Security Council, and IAEA officials say it is because ElBaradei fears the situation could escalate out of control and lead to military strikes.

P5+1 OFFERS

June 2006 - The United States, Russia and China join forces with the EU3 and decide to make a new offer to Iran. European Union foreign policy chief Javier Solana presents the Iranian government with an offer on behalf of the six powers. The group, referred to as the P5-plus-1 -- five permanent Security Council members and Germany -- make clear they will hold off on any Security Council action if Tehran halts enrichment work and agrees to negotiate with them.

The United States, which severed relations with Tehran in 1980, agrees to provide incentives as part of the package on offer to Iran as well, including civilian aircraft parts and information technology. Iran does not accept the offer.

June 2008 - The six powers agree to beef up their proposal.

SECURITY COUNCIL RESOLUTIONS AND SANCTIONS

July 2006 - The Security Council orders Iran in a legally binding resolution to halt its nuclear enrichment programme and other sensitive activities.

December 2006 - The Security Council passes a new resolution imposing travel restrictions and asset freezes on Iranian firms and individuals linked to Iran's nuclear and missile programmes for refusing to suspend enrichment work. The resolution also bans the export of equipment that could be used in Tehran's missile and nuclear programmes.

March 2007 - The Council passes a second sanctions resolution that expands the list of blacklisted Iranian individuals and firms and bans some weapons trade with Iran.

March 2008 - The Council adopts a third sanctions resolution against Tehran that expands the measures in place a bit further. It also urges vigilance regarding Iranian banks and asks U.N. member states to inspect some Iran vessels coming in and out of the country to look for banned items.

September 2008 - The Security Council passes a resolution that reiterates its commitment to resolving the nuclear standoff with Iran through diplomacy. It adds no new sanctions but reaffirms the three sanctions resolutions already passed.

FIRST GENEVA TALKS

July 2008 - U.S. Undersecretary of State William Burns joins his counterparts from the P5-plus-1 group and EU's Solana for a meeting with chief Iranian nuclear negotiator Saeed Jalili. The meeting is inconclusive and ends in deadlock.

SECOND GENEVA TALKS

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October 2009 - Burns returns to Geneva as President Barack Obama's Iran point man and a "full participant" in a new P5-plus-1 meeting with Jalili.

Iran agrees in principle to send low-enriched uranium to Russia and France for further processing and then have it returned for use at a Tehran medical reactor. But Iran later says it will not send enriched uranium abroad and instead will consider swapping it for nuclear fuel within its borders.

Tehran then misses an effective U.S. deadline of Dec. 31 to accept the plan.

(Editing by Jon Hemming)