The head of the United Nations’ atomic watchdog says that “the jury is still out” on negotiations between Iran and the U.S. over Tehran’s rapidly advancing nuclear program. But Rafael Mariano Grossi described the continuing negotiations a good sign. Grossi is the director-general of the International Atomic Energy Agency. He made the comment on Wednesday to journalists attending a weeklong seminar at the agency in Vienna. Grossi acknowledged one of his deputies was in Tehran on Wednesday. Iranian officials identified the official as Massimo Aparo. He is the head of the IAEA’s safeguards arm.