VIENNA (Reuters) - Iran has fired up advanced uranium-enriching centrifuges that it had installed underground at its Natanz site, in the latest breach of its nuclear deal with major powers, a report by the U.N. atomic watchdog obtained by Reuters on Wednesday showed. Natanz is Iran’s main uranium-enrichment site and the one that U.S. President Donald Trump recently asked for options on attacking, according to a source who confirmed a New York Times report. The deal states that Iran can only accumulate enriched uranium with first-generation IR-1 machines and that those are the only centrifuges it can operate at its underground plant at Natanz, apparently built to withstand aerial bombardmen