After the Arab Spring, the Iran nuclear file is back on President Barack Obama's desk with a potentially explosive report that found "credible" evidence that Iran had conducted nuclear weapons research in violation of its international commitments.
An International Atomic Energy Agency report contained the most comprehensive detail to date on Iran's nuclear programme, about which the agency said it had "serious concerns regarding possible military dimensions". However it did not produce a "smoking gun" and was unable to assert categorically that such research continues today.
Iran, a signatory of the Nuclear Non-Proliferation Treaty, has always denied that it is working on a nuclear weapon and insists that its nuclear programme is devoted to the production of electricity.
The IAEA report, reflecting the efforts of Western intelligence corroborated by IAEA inspectors, described work that it said could only have been related to developing weapons. It mentioned activities relevant to the development of a nuclear bomb trigger, the testing of high explosives and the design of a nuclear warhead.
However, much of the information in the report related to research pursued by Iran before 2003 when a US National Intelligence Estimate concluded that Iran had stopped work on a nuclear weapons programme. The view of the intelligence community remains that there is no hard evidence that the Iranian leadership has decided to build a nuclear weapon.