Iran may be withholding information needed to establish whether it tried to make nuclear arms, the International Atomic Energy Agency said Monday in an unusually strongly worded report. The tone of the language suggesting that Teheran continues to stonewall the agency - the UN nuclear monitor - revealed a glimpse of the frustration felt by agency investigators stymied in their attempts to gain full answers to suspicious aspects of Iran's past nuclear activities. Addressing whether Iran was complying with agency requests, the report said that "Iran has not provided the Agency with all the information, access to documents and access to individuals necessary to support Iran's statements" that its activities were purely peaceful in intent. "The Agency is of the view that Iran may have additional information, in particular on high explosives testing and missile related activities which ... Iran should share with the agency," said the report. It was referring to two alleged sets of tests that agency officials say could be linked to a nuclear program. The findings were part of a restricted agency report forwarded to the UN Security Council and to the 35 board members of the International Atomic Energy Agency that was obtained by The Associated Press. Asked whether Iran was stonewalling, a senior UN official familiar with Iran's nuclear file said that "it was evident" to agency investigators "that they may have some additional information" they were not providing. Iran already rejected evidence provided by the US and other IAEA board members on alleged weapons programs in February, but then promised to revisit the issue before the agency's next board meeting in a week. Its nuclear programs have been under International Atomic Energy Agency investigation since 2003, when a dissident group revealed the existence of a clandestine enrichment program. A senior US envoy suggested the report was a strong indictment of Iran's defiance of the international community's efforts to seek answers about troubling parts of its nuclear program, noting it "details a long list of questions that Iran has failed to answer." "At the same time that Iran is stonewalling its inspectors, it's moving forward in developing its enrichment capability in violation of Security Council resolutions," Gregory L. Schulte, the chief US delegate to the IAEA told the AP. He described parts of the report as a "direct rebuttal" of Iranian claims that all nuclear questions had been answered. Iran has described its cooperation with the agency probe of its alleged nuclear weapons experiments as positive, suggesting it was providing information requested by agency officials. Indirectly disagreeing, the agency also said that Iran continued to deny such activities, dismissing evidence to the contrary submitted for its perusal as misleading or false. The nine-page report also noted that Iran remains defiant of UN Security Council demands to stop uranium enrichment. Shrugging off three sets of council sanctions, Iran had instead expanded its operational centrifuges - machines that churn out enriched uranium - by about 500 since the last International Atomic Energy Agency report, in February, said the report. In announcing major progress in Iran's push for nuclear power, President Mahmoud Ahmadinejad said last month that Iranian scientists were putting 6,000 new uranium enriching centrifuges into place and testing a new type that worked five times faster. The report noted that Iran now had only 3,500 centrifuges and specified that the few advanced machines actually running were only in a testing phase. Still, the UN official said that the country's goal of 6,000 machines running by the summer was "pretty much plausible."