BOI - AFP - A timeline of the crisis over Iran's nuclear programme:

2002: An exiled Iranian opposition group says the country is building secret underground nuclear facilities, notably at Natanz in central Iran.
US President George W. Bush labels Iran, along with North Korea and Saddam Hussein's Iraq, as part of an "axis of evil."

The United States, which has not had diplomatic relations with Iran since 1979, seeks to dissuade Russia from helping the country build nuclear power plants.
Iran, which is a signatory of the nuclear Non-Proliferation Treaty (NPT), agrees that its sites, including Natanz, can be inspected by the UN's International Atomic Energy Agency (IAEA).

2003: UN inspectors say they have found traces of enriched uranium at Natanz. Tehran comes under pressure to sign an additional NPT protocol under which no-warning checks could be carried out on its nuclear sites; it agrees in principle.

2004: The disgraced head of Pakistan's nuclear weapons programme, Abdul Qadeer Khan, is reported to have helped Iran obtain equipment for enriching uranium in the 1990s.
Iran tests a new medium range missile which could easily attain Israel. The latter country is widely believed to have nuclear weapons, and is not a signatory of the NPT.
Tehran resumes work on enriching uranium and then agrees to suspend it during talks with Britain, France and Germany. The IAEA places seals on several of Iran's nuclear facilities.

2005: Mahmoud Ahmadinejad, a hardline populist, is elected president of Iran. Shortly after his accession, the country resumes uranium work.
US President George W. Bush makes the first of several statements in which he refuses to rule out the use of force to make Iran give up its nuclear programme.
Russia presents a plan, agreed to by the United States, that would allow Iran to continue uranium enrichment but on Russian soil. Talks take place, but fail early in 2006.

2006: Iran announces the resumption of nuclear research activities, and removes some of the IAEA seals on its plants. UN chief Kofi Annan urges Tehran to return to the negotiating table.
Iran engages in military maneuvers in the Gulf, including the testing of new missiles which could be used to block the oil route through the Straits of Hormuz. World oil prices jump on the news.
The United Nations Security Council gives Iran until April 28 to suspend enrichment, but the deadline passes without any change.
In April, reports in two US papers say that the United States is planning military attacks on Iran's atomic facilities, which could involve the use of nuclear weapons. Ahmadinejad says Iran will "cut off the hand of any aggressor".
On May 31, the United States makes a major policy shift, offering talks on condition that Iran suspended its uranium enrichment.