"Iran so far has not been forthcoming in replying to our questions, and we seem to be at a dead end there," said a senior UN official on Monday.
The report comes as speculation persists about an Israeli, or even American, strike against Iran's nuclear infrastructure to set back a program they insist aspires to build an atomic bomb. Iran says its sole ambition is to produce nuclear power.
"The IAEA has no interest in provoking a US confrontation with Iran," says Natalie Goldring, at the Security Studies Program at Georgetown University in Washington, noting the IAEA's history of detailed factual work.
"The unfortunate aspect of this sort of report is that it does encourage the hardliners of the Bush administration who would like 'do something' about Iran before leaving office."
"This is very high stakes, and I am somewhat surprised that the Iranians have proceeded in this direction," says Ms. Goldring. "I think the risks of conflict are unacceptably high, and I don't think either the US or Iran are helping with that."
In May, Tehran provided the UN with what it called a "final" 117-page presentation to address charges that it says resulted from forgeries to show weapons-related work in Iran. Since then, lack of Iranian cooperation has led to the impasse with the IAEA.
In Washington, news of the IAEA report provoked talk of additional sanctions against Iran.
The White House said the report showed "once again that Iran is refusing to cooperate with the international community," said spokesman Gordon Johndroe. Iran would face "further implementation of the existing United Nations Security Council sanctions and the possibility of new sanctions" if it did not suspend uranium enrichment, he said.
The US has led efforts to impose three rounds of UN sanctions against Iran and further US and European sanctions against Iran over its nuclear program.
UN Security Council resolutions require Iran to suspend all enrichment activities, but Monday's report notes that Iran has expanded the number of centrifuges enriching uranium to 3,820, up from 3,300 in May, and that some 2,000 more are being installed.
A senior Iranian official quoted by Reuters said the IAEA was to blame for the impasse and that the nuclear agency should work in a "legal and logical" manner.
Before the report was given to the 35-nation IAEA Board of Governors, an Iranian government spokesman said the IAEA should "conduct itself based on its own regulations and not be affected by outside pressure, including US pressure."
"We are always ready for the continuation of our cooperation within the confines of the modality for agreement," said Foreign Ministry spokesman Hassan Qashqavi.
"At the moment we haven't found a way forward with Iran, so that we can have the information that we need to assess the documents," said the senior UN official, briefing journalists in Vienna. "And as long as Iran is not ready to tackle this issue, to answer our questions, we cannot move forward."
The IAEA report verifies that no declared nuclear material has been diverted by Iran and that it continues to have no information "on the actual design or manufacture by Iran of nuclear material components of a nuclear weapon." But the IAEA takes Iran to task for lack of "any substantive progress" on several key issues of "serious concern."
"The agency encouraged Iran … to address the substance of the allegations with a view to dispelling the doubts which naturally arise, in light of all of the outstanding issues, about the exclusively peaceful nature of Iran's nuclear program," the report said.
Analysts at the Institute for Science and International Security in Washington wrote that the IAEA report showed that Iran is "making significant progress" in operating centrifuges and boosting enrichment rates, while it "continues to resist efforts to address substantively its alleged weapons-related work."
Further cooperation was important, the IAEA said, because Iran's answers last May "confirmed the veracity of some of the information" in the studies, the IAEA report said, though Iran "expressed concern" that resolving them would require IAEA access to sensitive conventional military and missile efforts.
While "expressing regret" that the IAEA could not provide Iran with copies of the material, the IAEA report said, it was "sufficiently comprehensive and detailed that it needed to be taken seriously."
"There has been no progress on the alleged studies. No information at all," says the senior UN official. "We would describe it as a gridlock."
The IAEA uses the term "alleged studies" to describe a collection of weaponization designs and documents – much of it coming from US intelligence agencies – that suggest Iran has tried to develop a nuclear warhead, modify a missile to carry a nuclear payload, and test high explosives underground and at distances consistent with a nuclear weapons test.
Iran says they are forgeries and for months refused to address them, though it cooperated to resolve a host of other issues identified by the IAEA and Iran in August 2007.
The IAEA report said inspectors meeting in Iran in August laid out concrete proposals to address the alleged studies, though Iran has yet to agree to them. Their aim is for Iran to "demonstrate credibly" that the activities are "not nuclear related, as Iran asserts, while protecting sensitive information" about conventional military efforts.
The proposals start with a request that Iran identify the "factually correct" part of the documents, as well as those that Iran considers fabricated.
May's 117-page presentation "was too much of a response in form and format, rather than in substance," said the senior UN official. Still, he indicated that the process with Iran was far from over. "It's clear that they start each meeting [with the IAEA] by saying that they have answered all the questions, but then they are ready to talk."