(CNN) -- Iran is still withholding critical information that could determine whether it is trying to make nuclear weapons, the International Atomic Energy Agency said in a restricted report.
Iranian technicians with an IAEA inspector near Tehran in 2005.
The nine-page report, obtained by CNN on Monday, detailed a number of recent meetings with Iranian officials who deny conducting weapons research and continue to stymie the United Nations' nuclear watchdog agency.
"The agency is continuing to assess the information and explanations provided by Iran," the report said. "However, at this stage, Iran has not provided the agency with all the information, access to documents and access to individuals necessary to support Iran's statements."
Iran has said its nuclear program is for peaceful purposes, namely energy for power lines, and in the past has described interactions with the IAEA as positive.
Tehran will continue to cooperate with the agency as it monitors the program, Foreign Ministry spokesman Seyed Mohammad Ali Hosseini said in response to the report, the semi-official Fars News Agency reported.
Fars said IAEA chief Mohamed ElBaradei "is expected to note progress" between the agency and Iran when he presents the report to the Board of Governors on June 2.
But the report, dated May 26, hints at the frustrations of the IAEA investigators seeking clear answers about the program.
The report said Iran still has not disclosed full information about its work on high-explosive testing and missile design work, as well as the "green salt project" studies -- research involving uranium tetrafluoride, a precursor to uranium hexafluoride, which is used in gas centrifuges to make enriched uranium.
"The agency has not detected the actual use of nuclear material" in the projects. However, they remain "a matter of serious concern," and clarification of them is critical to assessing Iran's past and present program, the report said.
The IAEA said some of its member nations had provided information on these programs. But Iran dismissed the allegations as baseless and argued that the evidence contradicting the agency's claims was fabricated, the report said.
Iran also rejected the IAEA's concerns about its work to develop a highly precise detonator that would be suitable for a nuclear weapon. Iran said the research was for civil and conventional military use, according to the report.
Still, Iran has remained open to the IAEA's surveillance and containment of nuclear material at its fuel enrichment plant.
Over the past year, IAEA investigators conducted 14 unannounced inspections of the facility, the report said.
Iran's nuclear program has spurred concerns by the United States and much of the West. In March, after the IAEA released a similar report on the program, the United Nations Security Council voted to impose new sanctions on Iran over its nuclear program.
That report said Iran had clarified many of the outstanding issues regarding its nuclear program, but that it had not suspended its activities related to enrichment of uranium, and that doubts remained about whether the country's program had a peaceful aim.
The latest U.N. sanctions against Iran tighten travel and trade restrictions on people and companies associated with the nation's nuclear program. The sanctions also allow searches of cargo suspected of carrying prohibited equipment and the monitoring of Iranian banks suspected of having links to proliferation activities.
Iran has condemned the resolution as "politically motivated" and "unlawful and illegitimate."