Iran’s nuclear chief is hinting at a compromise offer from Tehran ahead of negotiations with world powers this week over the country’s controversial atomic program. At the core of the dispute is the issue of uranium enrichment. The West fears Tehran is seeking an atomic weapon, which the country denies. Uranium has to be enriched to more than 90 percent to be used for a nuclear weapon. Iran’s nuclear chief Fereidoun Abbasi says Tehran could stop its production of 20 percent enriched uranium needed for a research reactor, and continue enriching uranium to lower levels for power generation. Abassi told state TV late Sunday that this could take place once Iran has stock piled enough of the 20 percent enriched uranium. The negotiations are to take place in Istanbul on Friday.