A senior Iranian official blamed the US Sunday for Teheran's refusal to respond to accusations it tried to make nuclear weapons, saying information provided by Washington was not only fake but came three years too late. Ali Ashgar Soltanieh, Iran's chief delegate to the International Atomic Energy Agency, also acknowledged that his country's uranium enrichment program - under sanctions by the UN Security Council - was experiencing "ups and downs." The comment appeared to be the first instance of Teheran admitting that its enrichment activities were running into some difficulties. The United States rejected being at fault. Gregory L. Schulte, Soltanieh's American counterpart, said "Iran did not need to wait for information to answer" the accusations coming at it from all sides that it was trying to make nuclear arms. "Iranian authorities could have started explaining these activities years ago, if only they had made the decision to come fully clean about their program." Schulte and Soltanieh spoke separately to The Associated Press in the wake of an IAEA report saying that suspicions about most past Iranian nuclear activities had eased or been laid to rest. But the report also noted that Iran had rejected documents that link it to missile and explosives experiments and other work connected to a possible nuclear weapons program, calling the information false and irrelevant. Calling weaponization "the one major ... unsolved issue relevant to the nature of Iran's nuclear programme," the report also confirmed that Iran is defying UN Security Council demands that it suspend enrichment, which can generate nuclear fuel and the fissile core of warheads. Most of the material shown to Iran by the IAEA on alleged attempts to make nuclear arms came from the US with some of its allies providing lesser amounts, diplomats told the AP, and the agency shared it with Teheran only after the originating nations gave their permission. But Soltanieh dismissed much of the material as counterfeit. In any case, he said, it came too late - three years after US intelligence claimed it had material allegedly on a laptop computer smuggled out of Iran indicating that Teheran had been working on details of nuclear weapons, including missile trajectories and ideal altitudes for exploding warheads. "They should have given it to us three years ago," Soltanieh said of the US material, suggesting Tehran would then have had a more substantive response. Instead, he said, Iran did not get an offer for a review until mid-February. By that time, he said, the deadline for the conclusion of the IAEA probe into Iran's nuclear past had passed and experts were already working on the agency's report.