A Russian official meanwhile confirmed that Iran is set to open a long-delayed nuclear reactor built by Russia, a step likely to fan Western fears that the Islamic republic could one day become a nuclear weapons power.

Russia is one of the five permanent members of the U.N. Security Council who have approved a draft resolution on a new set of sanctions against Iran that Washington circulated at the United Nations on May 18.

Iran could scuttle the deal to part with 1,200 kg of its low-enriched uranium (LEU) if the sanctions resolution is passed.

The draft resolution appeared to brush aside as too little and too late the surprise deal brokered by Brazil and Turkey the day before for Iran to send the LEU, potential nuclear bomb fuel, abroad in return for fuel rods to keep a Tehran medical research reactor running.

The first batch would arrive in Turkey within a month.

Such an arrangement was first mooted last October as a way, in Western eyes, to cut Iran's LEU stockpile below the minimum that would be needed for a nuclear weapon.