Under the landmark nuclear accord, certain US, European Union and UN sanctions are to be removed in exchange for Iran accepting long-term curbs on a nuclear program that the West has long suspected was aimed at creating a nuclear bomb.
A key provision of the agreement, negotiated by Iran with the United States, Britain, China, France, Russia and Germany, is Tehran's commitment to reduce its stockpile of low-enriched uranium to below 660 pounds (300 kg).
If much further refined, low-enriched uranium can yield fissile material for nuclear weapons.
"The shipment included the removal of all of Iran’s nuclear material enriched to 20% that was not already in the form of fabricated fuel plates for the Tehran Research Reactor," US Secretary of State John Kerry said in a written statement.
"This removal of all this enriched material out of Iran is a significant step toward Iran meeting its commitment to have no more than 300 kg of low-enriched uranium by Implementation Day," Kerry added.
Implementation Day refers to the date when the International Atomic Energy Agency, the Vienna-based UN nuclear watchdog, confirms Iran has taken a series of steps to curb its nuclear program, paving the way to US, EU and UN sanctions relief.
Kerry said the low-enriched uranium shipment would more than triple Iran’s "breakout time" of an estimated two-to-three months. "Breakout time" refers to the amount of time needed to obtain enough nuclear material to make a single atomic bomb.
With full implementation, the nuclear deal is supposed to push Iran's breakout time to at least one year.