Yukiya Amano's International Atomic Energy Agency has a team of experts monitoring known Iranian nuclear programs and probing suspicions that there might be other, undisclosed activities focused on nuclear weapons research and development.
Iran denies any interest in such arms and says it has never tried to develop them. It also dismisses concerns that it is enriching uranium for possible use as the core of a warhead, saying it wants only to produce reactor fuel. The agency says that its attempts to probe for evidence of suspected weapons research have been rebuffed for more than three years.
Israel in particular says the diplomatic window is closing as Tehran increases its capacity to enrich to a point that is only a step away from production of weapons-grade uranium. It says it will never tolerate an Iran capable of making such warheads, heightening fears that it may opt to strike the Islamic republic's nuclear facilities.
Amano told reporters that diplomatic efforts still have some traction. At the same time, it was the first time he expressed concern for the IAEA experts in Iran, telling reporters that his agency is "giving high priority for the safety of our inspectors and we are taking all the measures needed to protect them."
Asked for details, he said the pressure on the inspectors was "difficult to define," adding: "We need to protect our inspectors in order that they can discharge their responsibilities."
Ali Asghar Soltanieh, Iran's envoy to the IAEA, did not respond to phone messages seeking comment.
Earlier, Amano told a meeting of the IAEA's 35-nation board that he could not provide "credible assurance" for Tehran's claims that all of its atomic activities are peaceful because of insufficient cooperation with his agency—a concern he has expressed before.