The U.S. ambassador to the IAEA, Gregory Schulte, said the report on Iran's nuclear-related activities shows "in great detail how much Iran needs to explain, and how little it has" done so, AFP reported.
Schulte was commenting on the contents of the IAEA report that became available to news organizations in Vienna on May 26. In it, the IAEA said Iran is holding back information in several research areas that could be linked to its nuclear program.
The IAEA said Iran's research into the testing of high explosives and its work on missile-reentry vehicles are a matter of "serious concern." And it said Iran has not given it access to nuclear sites that the agency has requested to inspect.
The report said that "substantive explanations are required from Iran to support its statements on the alleged studies and on other information with a possible military dimension."
The new report is the latest in a series ordered by IAEA chief Muhammad el-Baradei in an attempt to resolve by diplomatic means the crisis between Iran and Western powers that accuse it of trying to develop a nuclear bomb.
U.S. envoy Schulte has said the report amounts to a direct rebuttal of Iran's assertions that it has answered all questions about it's nuclear program.
He said that at the same time as Iran is "stonewalling" IAEA inspectors, it has moved ahead with the development of enriched uranium in violation of UN Security Council resolutions.
In Washington, State Department spokesman Sean McCormack said the IAEA report is "disturbing" because it points to the Iranian military's involvement in the nuclear program. He said Iranian scientists are trying to fabricate what he called "hemispheres of uranium," which he said are the most suitable for weapons production.
"The IAEA and their experts took a look at this information, deemed that it was important information, and based on that they were going to present to the Iranian government a series of questions. I think they even presented to them, or showed them, some of the documents," McCormack said. "And thus far the Iranians have been willfully noncooperative. And you can read that in the report. It's disturbing, and we'll see what diplomatic next step will flow from this."
Uranium enrichment is a key part of the West's concern about Iran's nuclear program because, when sufficiently enriched, uranium can be used in weapons. A much lower level of enrichment makes it suitable for fuelling civil nuclear power plants, and this is what Iran says is all it seeks.
The IAEA report says that Iran has 3,500 uranium-enrichment centrifuges operational at its Natanz nuclear facility. The agency has previously said most of the centrifuges are of an old type based on 1970s technology. Tehran has said this number will soon be boosted to 6,000, presumably using a newer design which has already been tested at Natanz.
Iran's envoy to the IAEA, Ali Asghar Soltanieh, drew the opposite conclusion from the latest report as the United States. He said the report's conclusions are "a vindication and reiteration of the peaceful nature of Iran's nuclear activities," AFP cited the semi-official Fars news agency as reporting.
He said the report underlines that that there is no evidence of any diversion of nuclear materials to military purposes.
Soltanieh adds that Iran will continue with its uranium-enrichment program.
compiled from agency reports
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