"We started with measures that are practical and easy to implement, and then we move on to more difficult things," said Yukiya Amano, director general of the International Atomic Energy Agency.
"We certainly wish to include issues with 'possible military dimensions' in future steps ... We have already discussed it and will continue to discuss it at the next meeting" between the IAEA and Iran on February 8, he said.
A November 11 agreement with the IAEA towards improved oversight over Iran's programme included six steps such as this week's visit by IAEA inspectors to the Gachin uranium mine and to a new reactor plant at Arak in December.
Two years of talks between the IAEA and Iran over these accusations, detailed in a major and controversial IAEA report in November 2011 and consistently denied by Iran as being based on faulty intelligence, went nowhere.
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But Amano, 66, told AFP that Iran has not been let off the hook, saying that the November 24 accord with world powers made clear that "all past and present issues" must be resolved.
How long this takes "very much depends on Iran. It can be quick or it can be long. It really depends on their cooperation," he said.
Under the November 24 deal with world powers, Iran stopped for six months on January 20 enriching uranium to medium levels and began converting its stockpile of this material into a form much more difficult to process into weapons-grade.
This set the clock on Iran and the powers -- the United States, China, Russia, Britain, France and Germany -- negotiating a long-term "comprehensive" accord likely permanently reducing Iran's nuclear programme while removing UN and Western sanctions.