What does the resumption of the work refer to? [originaltext] Iran resumed u

Iran resumed ultra-sensitive nuclear work at its uranium conversion facility in Isfahan on Monday, a senior nuclear official said, a move that risks an international crisis. "Iran has resumed the conversion of uranium under the supervision of the International Atomic Energy Agency," the vice-president of Iran’s Atomic Energy Agency Mohammad Saidi told journalists. The resumption of ’the work puts Iran at risk of being hauled before the UN Security Council for possible sanctions.