Iran has begun enriching uranium with a second cascade of advanced IR-2m centrifuges in its underground plant at Natanz in breach of its deal with major powers, a U.N. nuclear watchdog report to member states obtained by Reuters on Tuesday showed.

Iran was already enriching with one cascade, or cluster, of 174 IR-2m machines underground at Natanz. It informed the International Atomic Energy Agency in December that it planned to install three more IR-2m cascades there, one of which is now online, the IAEA report dated Monday said.

'The Agency also verified that installation of the second of the aforementioned three (extra) cascades of IR-2m centrifuges was nearing completion and installation of the third of these cascades had started,' said the confidential report.