Iran has given UN inspectors key documents about activities that could be used to make a nuclear weapon and allowed them to question a senior official suspected of involvement in the program, diplomats and officials said Thursday. The International Atomic Energy Agency hoped Iran's recent decision to cooperate will shed light on whether the country's military engaged in secret uranium enrichment activities, the diplomats and officials told The Associated Press. They spoke on condition of anonymity because of the sensitivity of the investigation. At issue is how much centrifuge and related technology the country acquired on the black market starting in the 1980s and the location of the equipment - which can enrich uranium to low-grade fuel or the fissile core for nuclear warheads. There are suspicions that some of the material has not been declared to the IAEA and had been used by the military for a nuclear weapons program. A US official described Iran's decision to cooperate on the documents and permitting questioning of the official after nearly two years of foot-dragging as "important concessions." "You are chipping away at some of the issues," said the official. He emphasized, however, that Tehran still needed to meet IAEA requests for access to military sites which Washington has identified as possibly being used for nuclear arms-related experiments and other demands. For the Americans, however, Iran's readiness to cooperate is a mixed blessing. One of the diplomats said Iran's new willingness to cooperate on the enrichment issue - agreed to last week during a visit to Tehran by Olli Heinonen, an IAEA deputy secretary general - seemed to be directly calculated to reduce the threat of Security Council referral by weakening the argument that Iran was not cooperating with the IAEA probe. The Americans are the main proponents of having Iran hauled before the Security Council. They and their allies suspect Tehran's nuclear program - undetected for nearly two decades until three years ago - is a front for weapons ambitions. Iran says it is interested only in generating electricity. Another diplomat close to the IAEA cautioned against early optimism that that Iran's decision would quickly clear up suspicions about a military enrichment program so secret that even members of the civilian leadership did not know about it. He said the concession was "part of the process" and that there was still much to learn. Former agency officials also warned against setting expectations too high. One who is familiar with the process said IAEA questioning of Iranian officials was never one on one and the Iranian being interviewed was probably highly carefully briefed on what to divulge. All of those speaking to the AP declined to go into details about whom Heinonen was able to talk to and what documents he was given, saying such exposure could result in Iran breaking off its cooperation. Asked about the Iran investigation, IAEA spokeswoman Melissa Fleming said "the agency does not comment ongoing investigations until it's time to report to the (IAEA) board of governors." Underpinning suspicions about a secret military enrichment program are previous declarations by Iran that members of the black market network offered Iranian officials P-1 centrifuge designs in 1987 - only to offer the same designs seven years later to a different set of officials. The agency is also questioning claims by the Iranians that - while it received designs for the more advanced P-2 centrifuge in 1995 - it did not start development until 2002. That, say experts with former links to the agency may suggest secret work by the military that has not been declared to IAEA inspectors. A report prepared for the September board meeting by IAEA chief Mohamed El Baradei says as much, declaring the evidence provided to explain the gap does "not yet provide sufficient assurance that no related activities were carried out during that period."