The U.N. atomic agency chief says he can wrap up his probe of allegations that Iran worked secretly on nuclear arms by the end of the year but needs Tehran's cooperation to do so.

Yukiya Amano's comments Saturday were in line with his statement the day before on return from talks in Tehran. On Friday, he suggested that a meeting with Iranian President Hassan Rouhani has done little to advance his probe.

Amano, of the International Atomic Energy Agency , said Saturday that "more work will be needed" to kick-start the investigation — the same phrase he used Friday

The U.S. and its allies say the agency must deliver a ruling on the suspicions based on Iranian cooperation, as part of the overall nuclear deal now being negotiated.