U.S. Secretary of State John Kerry speaks to the media during a news conference at the United Nations Headquarters in Manhattan, New York, December 18, 2015. REUTERS/Eduardo Munoz

WASHINGTON (Reuters) - A ship carrying more than 25,000 pounds (11,000 kg) of low-enriched uranium materials left Iran for Russia on Monday in an Iranian step toward honoring a July 14 nuclear deal with major powers, the United States said.

Under the landmark nuclear accord, certain U.S., European Union and U.N. 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 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 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 U.N. nuclear watchdog, confirms Iran has taken a series of steps to curb its nuclear program, paving the way to U.S., EU and U.N. 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.