The chief of the U.N. nuclear regulatory agency said on Tuesday he understood Iran is working "at quite high speed" on implementing restrictions on its nuclear activities called for by an agreement with major powers that would lead to a lifting of sanctions.

"We understand that Iran is undertaking the preparatory steps at quite high speed," he told reporters, adding that the International Atomic Energy Agency would need time to verify those steps: "Not days, not months, weeks' time for us."