The U.N. atomic energy agency is preparing to wrap up a more than a decade-long probe of alleged nuclear weapons work by Iran, but its report will stop short of delivering a judgment on whether the suspicions are valid, the agency’s chief said Thursday.

The report by the U.N.’s International Atomic Energy Agency is meant to put the issue to rest after years of on-and-off attempts to investigate the allegations. The U.S. and its allies say Tehran conducted past research and development of such weapons. Iran says the accusations are based on false intelligence from its adversaries.

The issue has dominated IAEA meetings, contributed to U.N. Security Council resolutions against Iran and is now playing a role on whether sanctions against Tehran will be lifted under a nuclear deal that is expected to implemented early next year.

But the comments by IAEA chief Yukiya Amano made clear that his assessment will contain enough gray zones to leave the question unresolved.

The report “won’t be black and white,” Amano told reporters outside a meeting of the IAEA’s 35-nation board. Suggesting some questions remained unanswered, he described his report as a “jigsaw puzzle,” of which his agency has “pieces.”

While he said that it was up to board members to decide whether to close the investigation on the basis of his report, diplomats briefed on the investigation said Thursday that outcome was likely.

Formally, the report will help determine whether Iran gets relief from sanctions in exchange for paring back its atomic activities under an overarching July 14 deal Tehran signed with six world powers

Two diplomats said the U.S. and the five other powers that negotiated the July 14 nuclear deal with Iran were unlikely to be too critical at the risk of jeopardizing that agreement, although expectations are that Iran has continued to either deny the activities under investigation or insist that they were part of peaceful nuclear research. They demanded anonymity because they weren’t authorized to discuss the issue.

Amano said his report will be circulated among board members next week, with a special Dec. 15 meeting to be convened for a decision on whether to declare the investigation closed.

(AP)