The International Atomic Energy Agency said that Iran, which denies ever having sought nuclear weapons, has undertaken to implement five new "practical measures" by August 25.
These included two steps related to what the IAEA calls the "possible military dimensions" (PMD) of Iran's nuclear programme -- in other words efforts to design a nuclear bomb.
The announcement comes after an apparently largely fruitless fourth round of talks between Iran and six world powers in Vienna last week towards a comprehensive deal over Tehran's nuclear programme by a July 20 deadline.
That report said that the evidence it has been given, which the IAEA judges to be "overall, credible", indicated that Iran "carried out activities that are relevant to the development of a nuclear explosive device."
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Iran says that the trove of evidence presented by the IAEA on these activities, which the Vienna agency believes took place before 2003 and possibly since, is based on faulty intelligence provided by the CIA and Israel's Mossad.
The second is Iran providing "mutually agreed relevant information and explanations related to studies made and/or papers published in Iran in relation to neutron transport and associated modelling and calculations and their alleged application to compressed materials".
The 2011 IAEA report said that it was "unclear" how the application of such modelling studies could be used for "anything other than a nuclear explosive" and that it was "essential" that Iran provide an explanation.
In their mooted nuclear deal with Iran, the six powers want Tehran to reduce drastically its uranium enrichment activities, something which the Islamic republic is loath to do.