File-This April 4, 2011, file photo shows Director General of the International Atomic Energy Agency, IAEA, Yukiya Amano from Japan speaking during a news conference of the IAEA's Parties to Nuclear Safety Convention Hold Review at the International Center in Vienna, Austria. The head of the U.N. nuclear agency is heading to Tehran for high-level meetings as he tries to accelerate his probe of allegations that Iran worked in the past on nuclear weapons. Fredrik Dahl of the U.N's International Atomic Energy Agency said that Amano's meetings Sunday, Sunday, Sept. 20, 2015, are aimed at "clarifications of past and present outstanding issues" linked to the agency's probe. (AP Photo/Ronald Zak, File)