The International Atomic Energy Agency (IAEA) described Iran's alleged nuclear weapons projects in its most detailed report so far on the subject, released Tuesday, dpa reported.
Here are some highlights of the document, which is based on intelligence reports and other information from 10 countries, as well as Iranian scientific reports, satellite images and interviews with nuclear smugglers.
PROGRAMME MANAGEMENT: The Iranian programme involved senior officials and various entities, including the Defense Ministry and universities.
Secret activities started in the late 1980s and were halted in 2003 because of the Iraq war. The nuclear programme was later resurrected.
IRANIAN FOREIGN PURCHASES: Iran bought high-speed electronic elements useful for triggering a nuclear warhead, high-speed cameras to monitor experiments, and various measuring devices.
KEY BOMB COMPONENTS: Iran conducted advanced work on making uranium metal hemispheres of the kind used in weapons, based on a design provided by a senior Pakistani engineer, Abdul Qadeer Khan.
DETONATORS: The Islamic state has admitted to developing special detonators, claiming they were for civilian and non-nuclear military applications. The IAEA said Iran has yet to provide a specific reason why it needs these parts.
The detonators were tested in a deep shaft, in an experiment that the IAEA sees as preparation for a nuclear weapons test.
EXPLOSIVES SYSTEMS: Iran conducted at least one experiment with so-called multipoint initiation systems, which are used in weapons to ensure that highly-enriched uranium implodes smoothly and generates a maximum yield.
MODELLING: Engineers created physical and computer models of various components, suitable for use in nuclear weapons, and tested them.
Explosives were tested in a large metal container at the Parchin military site, 30 kilometres south of Tehran.
There are indications that calculations were done on the explosion of highly enriched uranium.
NEUTRON INITIATORS: Work was undertaken to make so-called neutron initiators. These small capsules contain nuclear material and are placed in the centre of a nuclear weapon to set off a chain reaction.
NUCLEAR MISSILE: Engineers worked progressively to turn a convetional Shahab 3 missile into a nuclear weapon. The IAEA says it has seen reports produced by these experts.