"Iran right now is not providing any access, any clarification with regards to the whole area of the possible military dimension," said ElBaradei who heads the International Atomic Energy Agency (IAEA).
"They are not following what the Security Council asked us to do, that is 'please clarify this issue'," he said at a conference in Paris.
Iran has faced three sets of UN Security Council sanctions over its refusal to freeze uranium enrichment activities but Tehran has pressed on with its controversial nuclear work.
The United States and other Western powers suspect that the Islamic republic's nuclear programme is a cover for developing an atomic bomb.
Iran, a leading OPEC oil producer, denies it is seeking nuclear weapons and says it aims to provide energy for its growing population when its reserves of fossil fuels run out.
"I think they are committed to have the technology know-how," ElBaradei said. "I'm not sure that they want to take the extra step of developing nuclear weapons."
ElBaradei, a Nobel peace laureate, said a "smart country" does not need to have a nuclear weapon, just the technology.
"All you need is the technology because you are sending the message to your neighbours and the rest of the world that 'I can do it, (but) I don't have to do it … I can continue to be within the (non-proliferation) regime but everybody knows I can do it in a few months'."
He also pointed to the creation of a "new environment" with the election of US President Barack Obama who has expressed a willingness to open direct talks with Iran and in return Tehran has made "some positive noises".
"I don't think it's too late," he added about negotiating with Tehran. "You need to provide Iran with security assurances, with incentives."
He added that he was "quite impressed" with Iran's supreme leader, the Ayatollah Ali Khamenei, whom he met in Tehran, saying he "follows all the details" of the nuclear programme and talks "in a strategic way … he talks in the long term."
ElBaradei was speaking at a conference in Paris organised by the Academie Diplomatique Internationale (ADI) and the the International Herald Tribune newspaper.
