U.N. nuclear chief Yukiya Amano is heading to Tehran as part of efforts to probe suspicions that Iran worked secretly on nuclear weapons.

Those attempts have been stymied for nearly two years of arguments over what can be seen, and who can be interviewed how many times by Amano's experts.

Iran in the past rejected the open-ended investigation Amano seeks. But Iran's new leadership has promised more cooperation than in the past. Amano said `'we aim to build'' on new ideas presented by Iran.

Amano left Sunday, shortly after Iran and six world powers ended separate talks that failed to seal a deal that would cap some of Tehran's nuclear work in exchange for selective lifting of sanctions on its economy.

Iran denies work on nuclear arms. (AP)