The report by the International Atomic Energy Agency said Tehran had still not provided information about two specific areas of the IAEA's investigation that it was supposed to do more than two months ago, Reuters reported.
The confidential document was issued to IAEA member states less than three weeks before a self-imposed Nov. 24 deadline for Iran and the six global powers to end a decade-old standoff over the Islamic Republic's atomic activities.
"Iran has not provided any explanations that enable the agency to clarify the outstanding practical measures," the IAEA report said.
It was referring to two steps that Iran had agreed to carry out by late August, to help clarify allegations of explosives tests and other activity that could be used to develop a nuclear weapons capability. Iran denies any nuclear weapons aims.
The continuing deadlock in the IAEA's long-running inquiry suggests that any renewed headway will probably have to wait until after the negotiations between Iran and the United States, Britain, China, France, Germany and Russia are concluded.
Western officials say Iran must step up cooperation with the IAEA to help clarify its concerns as part of a broader diplomatic settlement, suggesting that some of the relief from sanctions the oil-producing country seeks will depend on this.