By Mark Heinrich and Iain Rogers
The watchdog believes Iran is withholding information needed to explain "serious" intelligence material from 10 countries that it has pursued projects to build an atomic weapon.
"(We do) not seek to 'pry' into Iran's conventional or missile-related military activities. Our focus is clearly nuclear material and activities," International Atomic Energy Agency (IAEA) Director General Mohamed ElBaradei said.
"We need, however, to make use of all relevant information to be able to confirm that no nuclear material is being used for nuclear weapons purposes," he added in a speech at the start of a meeting of the IAEA's board of governors in Vienna.
"I again urge Iran to show full transparency and to implement all measures required to build confidence in the exclusively peaceful nature of its nuclear program at the earliest possible date," he told delegates.
A September 15 IAEA report detailed Iranian non-cooperation with agency requests for documents and access to sites to back up Iran's denials of the allegations. Senior U.N. officials said the IAEA had "reached gridlock" with Iran.
The intelligence material suggests Iran in the past linked projects to process uranium, test high explosives at high altitudes and modify the cone of a long-range Shahab-3 missile in a way that would fit a nuclear payload.
Iran says the intelligence is forged and sites the IAEA wants to examine are purely conventional military facilities any nation would keep off-limits on security grounds.
"SERIOUS CONCERN"
ElBaradei said he was confident a way could be found to let the agency do its work while respecting "Iran's legitimate right to protect the confidentiality of sensitive information and activities".
But he told the governors: "Regrettably the agency has not been able to make substantive progress (in clarifying) possible military dimensions to Iran's nuclear program. This remains of serious concern."
He said it would help if member states which provided the IAEA with documentation on the Iranian projects allowed the agency to share it in hard copy form with Iran. Tehran should then clarify which parts were right and wrong.
"Unless Iran provides such transparency … the agency will not be able to provide credible assurances about the absence of undeclared nuclear material and activities in Iran," he added.
The IAEA has struggled for six years to get to the bottom of Iran's nuclear work. The United States and European allies say Iran is just stringing U.N. investigators along while pushing ahead with a sensitive nuclear fuel enrichment program.
Enriched uranium can be used either in power plants or — if refined to a much higher degree — in a nuclear bomb, although Iran says its sole aim is to generate electricity.
Its ambassador to the IAEA, Ali Asghar Soltanieh, said there was no evidence of any diversion of nuclear material and activities for what he termed "prohibited purposes".
He accused the United States of putting a "stumbling block" in the way of the IAEA's work by not providing enough evidence to back up its claims about Iran's nuclear activities.
"We have to stop this process because it is putting the credibility of the (IAEA) in serious jeopardy," he told reporters on the sidelines of the Vienna meeting.
"Iran has not created any difficulty for access to all nuclear material and facilities. This will continue."
A Western diplomat said Iran's demands for more evidence were an effort to deflect attention from the "real problem", Iran's "failure to cooperate" with the IAEA.
Iran has slowly but steadily expanded its uranium enrichment campaign in defiance of Security Council demands.
It now has almost 4,000 centrifuge machines refining uranium with 2,000 more being installed, the IAEA report said. U.S. analysts said Iran seemed to be nearing the capacity to produce enough fuel for a nuclear weapon within two years.
(Editing by Mark Trevelyan)
