The International Atomic Energy Agency Director General Rafael Grossi has been speaking to reporters in Seoul, South Korea.
He said a decision on how long a moratorium on uranium enrichment that Iran must be bound by under any agreement with the US was a political decision, according to the Reuters news agency.
His comments come amid reports the US had proposed a 20 year moratorium on enrichment during the talks with Iran in Islamabad. Tehran reportedly countered offered a moratorium of five years instead.
