"Our technical experts have spent years painstakingly and objectively analyzing a huge quantity of information," Yukiya Amano told the IAEA Board of Governors.

"The Agency finds the information to be, overall, credible. It is consistent in terms of technical content, individuals and organizations involved, and time frames. The information indicates that Iran has carried out activities relevant to the development of a nuclear explosive device."

The information also indicates that, prior to the end of 2003, "these activities took place under a structured program, and that some activities may still be ongoing," he said.

Western powers and Israel suspect Iran of seeking to build nuclear weapons. Iran denies this, saying its program is of a civilian nature. Speculation has been building that Israel is considering a preemptive strike on Iran's nuclear facilities.

Amano said his report identified in detail the issues which Iran needs to address in order to restore international confidence in what it says is the exclusively peaceful nature of its nuclear program.

"I ask Iran to engage substantively with the Agency without delay and provide the requested clarifications regarding possible military dimensions to its nuclear program," he said.

The IAEA continues to verify the non-diversion of nuclear material declared by Iran under its Safeguards Agreement, Amano said.

"But, as Iran is not providing the necessary cooperation, including by not implementing its Additional Protocol, the Agency is unable to provide credible assurance about the absence of undeclared nuclear material and activities in Iran, and therefore to conclude that all nuclear material in Iran is in peaceful activities," he said.

"I urge Iran to take steps towards the full implementation of its Safeguards Agreement and its other obligations," the IAEA director said.