Such a deal would be significant because, according to an independent research group, Tehran appears to be running out of the material, which it needs to feed its uranium enrichment program.
The report was drawn up by a member nation of the International Atomic Energy Agency and provided Tuesday to the AP on condition that the country not be identified because of the confidential nature of the information.
In Washington, State Department spokesman Ian Kelly said, "the transfer of any uranium yellowcake ... to Iran would constitute a clear violation of UNSC sanctions."
"We have been engaged with many of our international nonproliferation partners on Iran's illicit efforts to acquire new supplies of uranium over the past several years," he said.
A senior U.S. official who spoke on condition of anonymity because he was talking about confidential information said Washington was aware of the intelligence report, but he declined to discuss specifics.
"We are not going to discuss our private consultations with other governments on such matters but, suffice to say, we have been engaged with Kazakhstan and many of our other international nonproliferation partners on this subject in particular over the past several years," he told the AP. "We will continue to have those discussions."
In New York, Burkina Faso's U.N. Ambassador Michel Kafando, a co-chair of the Security Council's Iran sanctions committee, referred questions Tuesday about a potential deal between Iran and Kazakhstan to his sanctions adviser, Zongo Saidou. Speaking in New York, Saidou told the AP that, as far as he knew, none of the U.N.'s member nations has alerted the committee about any such allegations.
"We don't have any official information yet regarding this kind of exchange between the two countries," Saidou said. "I don't have any information; I don't have any proof."
A senior U.N. official said the Vienna-based IAEA was aware of the assessment but could not yet draw conclusions. He spoke on condition of anonymity because he was discussing confidential information. A Western diplomat from a member of the IAEA's 35-nation board said the report was causing concern among countries that have seen it and was generating intelligence chatter. The diplomat also requested anonymity because he was barred from publicly discussing intelligence information.
A two-page summary of the report obtained by the AP said the deal could be completed within weeks. It said Tehran was willing to pay $450 million, or close to euro315 million, for the shipment.
"The price is high because of the secret nature of the deal and due to Iran's commitment to keep secret the elements supplying the material," said the summary, adding: "The deal is to be signed soon." An official of the country that drew up the report said "elements" referred to state employees acting on their own without approval of the Kazakh government.
After-hours calls to offices of Kazatomprom, the Kazakh state uranium company, in Kazakhstan and Moscow, were not answered. Iranian nuclear officials also did not answer their telephones.
Purified ore, or uranium oxide - known as "yellowcake" - is processed into a uranium gas, which is then spun and re-spun to varying degrees of enrichment. Low enriched uranium is used for nuclear fuel, and upper-end high enriched uranium for nuclear weapons.
Iran is under three sets of U.N. Security Council sanctions for refusing to freeze its enrichment program and related activities that could be used to make nuclear weapons. Tehran denies such aspirations, saying it wants to enrich uranium only to fuel an envisaged network of power reactors.
Any attempt to import such a large amount of uranium ore would be in violation of those sanctions, which ban exports to the Islamic Republic of all items, materials, equipment, goods and technology that could contribute to its enrichment activities.
In addition, transfers of uranium ore in quantities greater than 500 kilograms - 1,100 pounds - annually are subject to close scrutiny by the Nuclear Suppliers Group of countries exporting atomic technology and materials.
Tehran still has hundreds of tons of uranium hexafluoride - the gas that is spun by centrifuges into enriched uranium. But its stockpile of uranium oxide, from which the gas is derived, is thought to be rapidly diminishing.
The IAEA believes that Iran's rapidly expanding enrichment program has been built on 600 tons of uranium oxide imported from South Africa during the 1970s as part of plans by the former regime to build a network of nuclear reactors.
The Washington-based Institute for Science and International Security said earlier this year that, based on 2008 IAEA statistics, Iran had already used up close to three-quarters of its South African supply.
In a November report, the IAEA noted that Iran had stopped producing uranium gas from yellowcake in early August and said Iranian officials had notified the agency that the production facility was down for maintenance.
David Albright, head of the Institute for Science and International Security, said Tuesday that the facility at the city of Isfahan had produced very little uranium gas for about a year.
"They said it was closed for maintenance but the reality is they probably ran out of uranium," he said.
Kazakhstan is among the world's three top producers of uranium, accounting for more than 8,500 tons last year. Iran, in contrast is producing an estimated 20 tons a year - far too little to power even one large reactor let alone the network it says it wants to put in place.
Experts say it has amassed enough low enriched uranium to build at least two nuclear warheads, should it choose to. Albright estimated that Tehran theoretically could produce about 150 such weapons from 1,350 tons of yellowcake, as specified in the intelligence report, but said that was not necessarily why Iran wanted the material.
"They want to have a civilian nuclear program but on the other hand they want to have nuclear weapons capability and they are willing to risk international sanctions," he said.
Tehran built its nuclear program on purchases from the black market, with its present workhorse centrifuge based on the same basic model that it purchased from the illicit nuclear network of Pakistani scientist A.Q. Khan in the 1980s.
"Their modus operandi is smuggling and that continues," said Albright, alluding to numerous instances of Iranian attempts to import equipment banned by the U.N. Security Council that have surfaced from the time its secret program was discovered seven years ago to the present.
Adding to concerns, Iran has recently announced it plans 10 new enrichment plants. It belatedly revealed that it had been working on a secret facility in September, in an action Western officials describe as pre-emptive and driven by fears it was about to be found out.
Associated Press Writers John Heilprin at the United Nations and Matthew Lee in Washington contributed to this report.