The International Atomic Energy Agency (IAEA) on Tuesday published the clearest indications to date that Iran has been developing a nuclear weapon, dpa reported.
"The information indicates that Iran has carried out activities relevant to the development of a nuclear explosive devices," IAEA chief Yukiya Amano said in the report obtained by dpa.
He was referring to information received from intelligence agencies and partially confirmed through other sources.
The report detailed a large number of nuclear-related projects and experiments and said that some of the activities might be ongoing.
A senior diplomat, who is closely following the IAEA's investigation, said all indicators for the key components of a weapons programme were contained in the document.
"They have been working on almost all areas that are there," he said.
Under the leadership of the Defence Ministry, scientists and engineers developed and tested components for a nuclear weapon, including so-called neutron initiators that set off nuclear chain reactions, the report said.
An IAEA member state informed the agency that this work may have continued as late as last year, it continued.
The Islamic state may also have prepared nuclear tests, by testing special detonators in an underground shaft.
In addition, Iranian experts modelled and calculated nuclear explosions of highly enriched uranium, according to information from two countries.
"The application of such studies to anything other than a nuclear explosive is unclear to the Agency," Amano wrote.
The report did not describe any experiments involving actual highly enriched uranium.
Iran received the design for the warhead from the smuggling network led by Pakistani engineer Abdul Qadeeer Khan, which also supplied Libya's secret nuclear arms programme, the report said.
However, the country also got help from other countries.
Amano wrote that his inspectors have interviewed a foreign explosives expert, who has been identified as Russian in several media reports.