February 23, 2017 0922 GMT
Two senior diplomats said the transfer recently approved by the US and five other world powers that negotiated the nuclear deal with Iran foresees delivery of 116 metric tons (nearly 130 tons) of natural uranium, AP reported.
UN Security Council approval is needed, but a formality, considering five of those powers are permanent Security Council members, they said.
Uranium can be enriched to levels ranging from reactor fuel or medical and research purposes to the core of an atomic bomb. Iran says it has no interest in such weapons and its activities are being closely monitored under the nuclear pact to make sure they remain peaceful.
Tehran already got a similar amount of natural uranium in 2015 as part of negotiations leading up to the nuclear deal, in a swap for enriched uranium it sent to Russia. But the new shipment will be the first such consignment since the deal came into force a year ago.
The diplomats, whose main focus is Iran's nuclear program, demanded anonymity Monday because they are not allowed to discuss the program's confidential details.
They spoke ahead of a meeting on Tuesday in Vienna of representatives of Iran, the United States, Russia, China, Britain, France and Germany to review Iranian complaints that the US was reneging on sanctions relief pledges included in the nuclear deal.
Prior to the Tuesday meeting, Iranian experts met their counterparts from other delegations, including the Americans, Press TV reported.
This time, the commission is convening at Iran’s request to address Washington’s decision to extend an anti-Iran sanctions law, a move Tehran has slammed as a violation of the nuclear deal.
The report by AP added that the diplomats said any natural uranium transferred to Iran after the deal came into effect would be under strict surveillance by the UN's International Atomic Energy Agency for 25 years after implementation of the deal.
They said Tehran has not said what it would do with the uranium but could choose to store it or turn it into low-enriched uranium and then export it for use as reactor fuel.
Without confirming the reported agreement, US officials argued that such shipments would neither endanger nor violate the Iran nuclear deal.
State Department spokesman John Kirby told reporters there was no prohibition on such imports by Iran and noted natural uranium "cannot be used ... for a weapon" in its original form.
White House spokesman Josh Earnest said such arrangements are "subject to the careful monitoring and inspections that are included in the deal to ensure that Iran is living up to the commitments that they made."