"It is true that we have had some engagement from Iran on issues with possible military dimension. But in the past several months, progress is very limited," Yukiya Amano, the head of the agency said on Monday on the sidelines of a conference on nuclear proliferation.
His remarks come as US Secretary of State John Kerry is to return to Switzerland for talks Thursday with his Iranian counterpart Mohammad Javad Zarif on a deal to restrain Tehran's nuclear program, Kerry's office said.
Kerry's return to Lausanne will again feed speculation that the top world powers represented in the "P5+1" group are nearing an agreement with Tehran, with a March 31 deadline looming to agree to the outlines of a deal.
The complex deal on the table would likely involve Iran reducing its nuclear activities, allowing tight inspections, and limiting development of new nuclear machinery.
In exchange, Iran -- which denies wanting nuclear weapons -- would get relief from the mountain of painful sanctions that have strangled its oil exports and hammered its economy.
The IAEA for years has been investigating the possible military dimensions (PMD) of the Iranian nuclear program. "We need to accelerate that clarification," Amano said. "But the fact is that progress is limited.''
"I think the clarification of the issues of PMDs is needed to enhance the confidence in Iran's nuclear activities," he said. The Japanese diplomat sounded upbeat about the potential for an agreement being implemented -- if one is reached.
"If a new agreement is agreed, it is the interest of Iran to implement it. ... We may have some problems from time to time. That happens with any country. We don't have particular reason that it will not be implemented."