IAEA Secretariat reported that "the Agency has not seen indications of diversion of nuclear material to nuclear weapons or other nuclear explosive devices ... however, after three years of intensive verification, there remain uncertainties with regard to both the scope and the nature of Iran's nuclear programme". However, the inspectors did find some sensitive documents, including instructions and diagrams on how to make uranium into a sphere, which is only necessary to make nuclear weapons. Iran furnished the IAEA with copies, claiming not to have used the information for weapons work, which it had obtained along with other technology and parts in 1987 and the mid-1990s. It is thought this material was sold to them by Abdul Qadeer Khan, though the documents did not have the necessary technical details to actually manufacture a bomb. On 18 December 2003, Iran voluntarily signed, but did not ratify or bring into force, an Additional Protocol that allows IAEA inspectors access to individuals, documentation relating to procurement, dual-use equipment, certain military-owned workshops, and research and development locations. Iran agreed voluntarily to implement the Additional Protocol provisionally, however when the IAEA reported Iran's non-compliance to the United Nations Security Council on 4 February 2006 Iran withdrew from its voluntary adherence to the Additional Protocol. On 12 May 2006, claims that highly enriched uranium (well over the 3.5% enriched level) was reported to have been found "at a site where Iran has denied such sensitive atomic work", appeared. "They have found particles of highly enriched uranium [HEU], but it is not clear if this is contamination from centrifuges that had been previously found [from imported material] or something new," said one diplomat close to the UN International Atomic Energy Agency (IAEA). These reports have not yet been officially confirmed by the IAEA (as of 1 June 2006). On 31 July 2006, the United Nations Security Council passed a resolution demanding that Iran suspend its uranium enrichment activities. In late 2006, "New traces of plutonium and enriched uranium– potential material for atomic warheads– have been found [by the IAEA] in a nuclear waste facility in Iran." However, "A senior U.N. official who was familiar with the report cautioned against reading too much into the findings of traces of highly enriched uranium and plutonium, saying Iran had explained both and they could plausibly be classified as byproducts of peaceful nuclear activities." In 2007 these traces were determined to