U.S. media are reporting that the Obama administration and other global powers have approved a large shipment of natural uranium from Russia to Iran in an exchange authorized by the Iran nuclear deal.

Diplomats told the Associated Press and Fox News that the transfer recently agreed by the United States and five other world powers that negotiated the nuclear deal with Iran foresees delivery of 116 metric tons of natural uranium.

The transfer needs U.N. Security Council approval but just as a formality, considering five of those powers are permanent Security Council members, the diplomats said, according to Fox News.

The natural uranium agreement comes at a sensitive time. With the incoming U.S. administration and many U.S. lawmakers already skeptical of how effective the nuclear deal is in keeping Iran's nuclear program peaceful over the long term, they might view it as further evidence that Tehran is being given too many concessions.

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 this week in Vienna of representatives of Iran, the United States, Russia, China, Britain, France and Germany to review Iranian complaints that the U.S. was reneging on sanctions relief pledges included in the nuclear deal.

The diplomats said any natural uranium transferred to Iran after the deal came into effect would be under strict surveillance by the U.N.'s International Atomic Energy Agency for 25 years after implementation of the deal.