Iran ? A new report by the U.N.’s nuclear watchdog raises “very troubling questions” about Iran’s engagement in weapons production and will open a new page in the probe into Tehran’s alleged activities, a senior U.S. official said Thursday.

The International Atomic Energy Agency released a report last week saying that suspicions about most past Iranian nuclear activities had eased. But it also pointed to Tehran’s continuing efforts to enrich uranium.

It called weaponization “the one major … unsolved issue relevant to the nature of Iran’s nuclear program.”

In an interview with Associated Press Television News, Gregory L. Schulte, the top U.S. delegate to the IAEA, said the report will “open a whole new page in our investigation because it raises very troubling questions about Iran’s engagement in weaponization activities.”