Iran's foreign ministry and the Iranian nuclear agency rejected the report, calling it "politically motivated" in a joint statement.

Iran carried out secret nuclear activities with material not declared to the UN nuclear watchdog at three locations that have long been under investigation, the watchdog said in a wide-ranging, confidential report to member states seen by Reuters.

The preliminary U.S. proposal came as a confidential U.N. report described an Iranian initiative that had multiplied Tehran’s stockpile of near-bomb-grade uranium.