The preliminary U.S. proposal came as a confidential U.N. report described an Iranian initiative that had multiplied Tehran’s stockpile of near-bomb-grade uranium.

Iran has further stepped up its production of highly enriched uranium, according to the UN nuclear watchdog. In a confidential report seen by the BBC, the International Atomic Energy Agency (IAEA) said Iran now possesses over 400kg of uranium enriched to 60% purity - well above the level used for civilian purposes and close to weapons grade,

Iran has increased production of highly enriched uranium, according to the United Nations nuclear watchdog, as the nation conducts talks with the United States on a nuclear deal.