Several times Iran postponed the resumption of uranium conversion, which can be a step towards fashioning a nuclear bomb, while Britain, France and Germany, with American support, worked on a package of economic and political incentives for Iran to give up its nuclear plan.

NPR: Iran's Leader May Favor a Showdown

It recently confirmed it had resumed the conversion of medium enriched uranium into oxide fuel to slow down growth of its stockpile.

BBC: The clock is ticking on Iran

All mined uranium is used domestically, after conversion and enrichment abroad.

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The most obvious attempt was when we gave them an offer that said we are going to provide the conversion of some of the low-enriched uranium that they already have into the isotopes that they need for their medical research and for hospitals that would serve up to a million Iranian citizens.

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The HEU Agreements provide for the conversion of approximately 500 metric tons of highly enriched uranium contained in Russian nuclear weapons into low-enriched uranium for use as fuel in commercial nuclear reactors.

WHITEHOUSE: Executive Order--Russian Highly Enriched Uranium

The other is an agreement on a proposal to take Iran's stockpile of low-enriched uranium (LEU) and send it to Russia and France for conversion into fuel rods for use in Iran's small research reactor in Tehran, which produces isotopes for cancer treatment.

BBC: Iran nuclear crisis: are new sanctions on the way?