The United Nations said Iran had defied a Security Council resolution aimed at curbing its nuclear program. The International Atomic Energy Agency watchdog group issued a report Thursday after the expiration of a 60-day grace period granted by the Security Council for Iran to halt uranium enrichment, a process that can be used for bomb-making. According to the report, Iran has ignored Security Council Resolution 1737 of late December by building two new networks of uranium centrifuges in one of its nuclear plants, apparently in a bid to achieve “industrial scale” enrichment. The IAEA report empowers the Security Council, which already has imposed limited sanctions on Iran, to discuss broadening them. Israeli officials have said Iran is not as close to attaining the means to build nuclear weapons as it pretends and that effective international pressure can still rein it in.