Timeline of Iran's nuclear crisis

July 1968
Under the reign of Shah Mohammad Reza Pahlavi, Iran signs the Nuclear Nonproliferation Treaty (NPT) which currently has 189 signatories. Only four countries have not signed the treaty: India, Israel, North Korea and Pakistan.

February 1979
The Iranian Revolution overthrows the Shah. Work on the Bushehr reactor is frozen, as is nuclear energy cooperation with the US, France and other Western nations.

1984 – 1987 Iran-Iraq War
Arch foe Iraq repeatedly bombs the Bushehr reactor site, destroying existing reactors.

September 1985
Foreign ministers of Iran, Syria and Libya declare that it is vital for their countries to develop nuclear weapons as a security deterrent to nuclear Israel.

September 2002
Construction begins on Iran’s first nuclear reactor at Bushehr since the destruction of the site during the Iran-Iraq War. Despite US objections, Russian engineers provide nuclear expertise for the project.
 
December 2002
US satellite photos capture images of sites at Natanz and Arak. While the Arak site houses a heavy water plant, Natanz has a nuclear enrichment facility, making it the crux of Iran’s future disputes with the international community.

February 2003
Iranian President Mohammed Khatami reveals that Iran has unearthed uranium deposits and announces plans to develop a nuclear fuel cycle. Khatami announces the existence of the Natanz facility and other sites and invites the International Atomic Energy Agency (IAEA) to visit them. Iran removes IAEA seals and cameras in its nuclear facilities.

June 2003
Following a trip to Iran, IAEA chief Mohammed ElBaradei accuses Tehran of not revealing the extent of its nuclear work.

August 2005
Iranian President Mahmoud Ahmadinejad takes office and pledges an "irreversible" resumption of enrichment.

July 2006
The UN Security Council adopts Resolution 1696 calling on Iran to halt its uranium enrichment programme.

December 2006
Iran’s failure to respond satisfactorily to Resolution 1696 leads to the adoption of UN Security Council Resolution 1737, which imposes sanctions against Iran banning the supply of nuclear-related technology and materials. Under the sanctions, the assets of key individuals and companies related to the enrichment programme are frozen.

March 2008
The UN Security Council adopts Resolution 1803 requiring Iran to stop all forms of uranium enrichment. It also calls on Iran to stop any research and development associated with centrifuges and uranium enrichment.

September 2009
Just days before the annual UN General Assembly meeting, Iran admits to having a secret uranium enrichment site at Qom. It is the second site of its kind made public after Natanz and triggers renewed alarms over Iran’s nuclear ambitions.

February 2, 2010
In a televised speech, President Ahmadinejad says Iran would have ”no problem” with an international plan that would see most of Iran’s low-enriched uranium sent abroad to be enriched to 20%.

February 7, 2010
Iran's atomic chief Ali Akbar Salehi tells state media that Iran has started enriching uranium to 20%, going back on Ahmadinejad’s apparent acceptance of the proposal to have uranium enriched abroad. World powers – especially the US and France – push for new UN sanctions in response to the news.

March 1, 2010
On a visit to Paris, Russian President Dmitry Medvedev says he is ready to accept new sanctions against Iran, provided they do not "target the (civil) population." On March 31, China, another permanent member of UN Security Council, also agrees to negotiate on new sanctions.

May 17, 2010
Brazil and Turkey broker an agreement whereby Iran will exchange its uranium for reactor fuel. According to the agreement, Tehran will send Turkey 1,200 kg of low enriched uranium in exchange for 120 kg of 20-percent enriched uranium. But Iran adds it will still continue to enrich uranium to 20 percent in its territory.

June 8, 2010
After months of negotiations, the five permanent members of the UN Security Council agree on a new sanctions regime against Tehran. The Security Council plans to table a vote the following day. If passed, it will be the fourth round of UN sanctions on Iran in as many years.