Washington says a ship carrying more than 11,000 kilograms of low-enriched uranium material left Iran for Russia on December 28 in a major Iranian step toward fulfilling its commitments in a landmark nuclear deal with major powers.
"The shipment included the removal of all of Iran's nuclear material enriched to 20 percent that was not already in the form of fabricated fuel plates for the Tehran Research Reactor," U.S. Secretary of State John Kerry said in a statement.
Kerry called it a "significant step."
As part of the July 14 nuclear deal, Iran must ship out all except 300 kilograms of the low-enriched uranium it has stockpiled.
Low-enriched uranium is suited to power generation but can be further enriched to arm nuclear warheads. Its removal is a key obligation by Iran under the deal.
The July agreement also commits Iran to sharply reduce the number of centrifuges, which can be used to enrich uranium, as well as to reengineer a reactor to cut its output of plutonium.
Iran is also committed to either export the near-20 percent supply, process it into low-enriched uranium, or turn it into fuel plates to power a research reactor.
In exchange for those and other conditions meant to constrain Iran's ability to make nuclear weapons, most international sanctions imposed on Tehran over its nuclear programs will be lifted.
Iran maintains it has no plans to make nuclear weapons.