The U.S. Treasury on Monday suspended some of its sanctions against Iran, after the Islamic Republic began halting its most sensitive nuclear activity as part of a groundbreaking agreement with Western powers.



The confidential report by the International Atomic Energy, obtained by Reuters, said Iran had begun diluting its stockpile of uranium enriched to the fissile concentration of 20 percent - a level that took it closer to the capability of producing fuel for an atom bomb.



The U.S. Treasury said hours following news of the Iranian move that it has suspended sanctions on foreigners engaged in transactions related to Iran's oil exports, and some trade in gold and precious metals.



The IAEA report to member states said: "The Agency confirms that, as of 20 January 2014, Iran ... has ceased enriching uranium above 5 percent U-235 at the two cascades at the Pilot Fuel Enrichment Plant (PFEP) and four cascades at the Fordow Fuel Enrichment Plant (FFEP) previously used for this purpose."



It was referring to Iran's two enrichment plants, at Natanz and Fordow. Cascades are interlinked networks of centrifuge machines that enrich uranium. Iranian state television earlier said Iran had suspended 20 percent enrichment at Natanz and that inspectors were heading to Fordow.



"The suspension of 20 percent enrichment has started at the Natanz plant and the International Atomic Energy Agency inspectors are going to the Fordow plant," state TV quoted the deputy head of Iran's Atomic Energy Organization, Behrouz Kamalvandi, as saying.



The IAEA report also listed other measures Iran had agreed to under the interim accord with the six world powers - the United States, France, Britain, Germany, China and Russia.



Those included an undertaking that Iran would not build any more enrichment sites during the six-month agreement, a step meant to buy time for negotiations on a final settlement of Tehran's decade-old nuclear dispute with the six powers.

Enriched uranium can have both military and civilian purposes. Iran denies Western allegations that it has been seeking to develop the capability to make nuclear bombs, saying it wants only civilian atomic energy.

Meanwhile, UN Secretary General Ban Ki-moon announced late Sunday in New York that he had invited Iran to attend this week's international peace talks in Switzerland on the Syrian conflict. The participation of Tehran, a close ally of Syrian President Bashar Assad, has been a sticking point in the long-delayed peace conference.