President Mahmoud Ahmadinejad on Wednesday ordered Iran to "go build" four more nuclear research reactors in addition to the sole one operating in Tehran.

"It has been estimated that four nuclear reactors in four different spots in the country are needed. Go build them, to carry out research activities and provide radio-medicine needed by the country," he said in a speech on state television.

The order came after Ahmadinejad unveiled a number of advances in Iran's controversial nuclear programme that served as a defiant blow to international efforts to rein in its atomic activities.

Iran is currently building one other research reactor, a heavy-water facility in the central city of Arak designed to be more powerful than the ageing Tehran research facility built in 1967 by America.

It also has projects to construct 20 reactors to produce electricity.

Iran's nuclear drive has unsettled the West and Israel, which fear it could include work towards atomic weapons.

Tehran has denied its programme is anything but peaceful.

However the International Atomic Energy Agency, the UN's nuclear watchdog, said in November it had evidence of tests and computer simulations that strongly suggested a military dimension to Iran's activities.

Iran nuclear crisis timeline
Tehran (AFP) Feb 15, 2012 - Key developments in the standoff over Iran's nuclear programme:

2005

- Aug 8: Iran resumes uranium conversion activities which had been suspended since November 2004.

2006

- April 11: Iran says it has enriched its first uranium to 3.5 percent purity and later, in May, to 4.8 percent. This is insufficient to make a nuclear bomb.

- Dec 23: The UN Security Council imposes sanctions on Iran's trade in sensitive nuclear materials and technology. It strengthens the measures in 2007 and 2008.

2007

- April 9: President Mahmoud Ahmadinejad says Iran can produce nuclear fuel on an industrial scale.

2009

- April 9: Iran inaugurates its first nuclear fuel plant, and says it has installed 7,000 uranium enrichment centrifuges at Natanz.

- Sept 25-28: Iran reveals a secret uranium enrichment plant, Fordo, which is being built inside a mountain near the holy city of Qom.

2010

- June-July: World powers enact new military and financial sanctions.

- July 30: Iran says it is ready for immediate talks with the United States, Russia and France over an exchange of nuclear fuel.

- Aug 16: Iran announces it is to start building its third uranium enrichment plant in early 2011.

- Aug 21: Iran starts loading fuel into its Russian-built first nuclear plant at Bushehr.

- Nov 29: Twin blasts in Iran's capital kill a top nuclear scientist and injure another. Ahmadinejad blames Israel and the West.

2011

- Jan 22: Failure of new talks between Tehran and six world powers in Istanbul.

- July 19: Iran says it has begun installing new centrifuges with better quality and speed.

- Aug 22: Iran says it has begun transferring centrifuges from Natanz to the Fordo underground site.

- Sept 2: The IAEA says it is getting worried about a possible military dimension to Iran's nuclear activities. It says since February 2007, Iran has produced more than 4,500 kilos (9,900 pounds) of 3.5-percent enriched uranium at its Natanz site.

- Nov 8: An IAEA report points to "serious concerns" about Iran's nuclear activities, and "credible" information Tehran may have worked on developing atomic weapons.

- Dec 27: Iran warns that no oil will pass through the key oil transit Strait of Hormuz if the West applies sanctions on its oil exports. The US warns Tehran it will not tolerate any attempt to disrupt shipping there.

- Dec 31: US President Barack Obama signs into law tough new sanctions targeting Iran's central bank and financial sector.

2012

- Jan 1: Iran says its scientists have "tested the first nuclear fuel rod produced from uranium ore deposits inside the country."

- Jan 9: The IAEA confirms that Iran has started enriching uranium at Fordo.

- Jan 11: An Iranian nuclear scientist is killed in a Tehran car bomb assassination, the fourth scientist killed in two years.

- Jan 23: The EU announces a ban on Iranian oil, along with sanctions against Iran's central bank.

- Jan 24: Obama says that a peaceful outcome is still possible in the nuclear standoff.

- Jan 26: Ahmadinejad again says Tehran is ready to sit down for talks.

- Feb 15: Ahmadinejad unveils what is said to be Iran's first domestically produced, 20-percent enriched nuclear fuel for Tehran's research reactor and says 3,000 more centrifuges had been added to the uranium enrichment effort.

Iran also activated a new generation of centrifuges that it said increased its enrichment capacity by three times.

The EU confirms it has received a letter from Iran proposing to resume nuclear talks and says it is "carefully studying" it.