VIENNA - Iran appears to be holding back growth of its most sensitive nuclear stockpile by continuing to convert some of it into reactor fuel, diplomats said on Monday, potentially giving more time for negotiation with world powers.
The stock of medium-enriched uranium gas is closely watched in the West; Israel has threatened to attack if diplomacy fails to curb Iran's program and it amasses enough of the material - a short technical step from weapons-grade - to make a bomb.
Since Iran in 2010 began enriching uranium to a 20 percent concentration of the fissile isotope, it has produced more than the 240-250 kg that would be needed for one weapon.
But it has kept the stockpile below the stated Israeli "red line" by converting part of the uranium gas into oxide powder in order, it says, to yield fuel for a medical research reactor.
The diplomats, accredited to the United Nations' International Atomic Energy Agency (IAEA), said Iran might even have stepped up this conversion in recent months.