Director General Yukiya Amano of the International Atomic Energy Agency told CNN that Iran has only informed the agency about facilities and activities intended for peaceful purposes.
"But there are also, there may be other facilities which are not declared, and we have the indication or information that Iran has engaged in activities relevant to the development of nuclear explosive devices," Amano said in Vienna Wednesday.
In a related development, a Western diplomat said the five permanent members of the U.N. Security Council along with Germany have agreed on a joint statement about Iran that will be delivered to the IAEA Thursday.
The diplomat said the statement underlines concerns about Iran's nuclear activities, including uranium enrichment at Natanz and Fordow.
The statement is notable, the diplomat said, because it represents a unified message.