“Iran has yet to provide explanations that enable the agency to clarify two outstanding practical measures,” Yukiya Amano told the body’s Board of Governors in Vienna, echoing a report seen by Reuters last month.

Diplomats have voiced doubt over whether the outstanding issues in the U.N. investigation would be resolved before a deal is reached between Iran, the United States, Britain, France, China, Russia and Germany, Reuters reported.

Xinhua news agency quoted IAEA chief as saying in a statement to the board meeting in Vienna on Monday: “The agency is not in a position to provide credible assurance about the absence of undeclared nuclear material and activities in Iran, and therefore to conclude that all nuclear material in Iran is in peaceful activities.”

He added that his agency remained ready to accelerate the resolution of all outstanding issues, but “this process cannot continue indefinitely”.