The United Nations nuclear watchdog chief says Iran has cut its stock of higher-enriched uranium that is closest to atomic weapons-grade.
The head of the International Atomic Energy Agency, Yukiya Amano, said Monday that Iran had "reached the halfway mark" in efforts to dilute half its 20 percent-enriched uranium to a lower grade suitable for use as reactor fuel.
Under an interim deal with the six world powers, the other half of the uranium is to be changed into a form that is relatively difficult to reconvert to 20 percent.
Uranium enriched to 20 percent is only a technical step away from the 90-percent level needed for weapons.
The IAEA has a pivotal role in checking that Iran is living up to its part of the six-month accord in curbing its disputed nuclear program in exchange for some easing of sanctions that have impaired its oil-dependent economy.
The deal, reached last year in Geneva, was designed to buy time for negotiations on a final settlement of the decade-old stand-off over nuclear activity that Iran says is peaceful but the West fears may be aimed at developing a nuclear bomb capability.
Expert-level talks between the sides are to be held in Vienna March 5-7.
In return for implementing the agreement, Iran is gradually winning access to $4.2 billion of its oil revenues frozen abroad and some other sanctions relief.
The funds will be paid out in eight transfers on a schedule that started with a $550 million payment by Japan on February 1. Last month, banking sources said South Korea was set to make two payments in March totaling $1 billion.
Some information for this report was provided by AP and Reuters.