"This (trigger) mechanism must be abandoned as an irrational principle in the event of further negotiations," Ali Akbar Velayati, a top adviser to Khamenei, said in an interview posted on the Supreme Leader's website.
"From the beginning, the Supreme Leader was not satisfied with the issue of the trigger mechanism and this was done against his will," said Velayati, a former foreign minister.
Iran has rejected Western calls for wider international talks over its nuclear and military ambitions after US President Donald Trump withdrew from the deal in 2018 and reimposed sanctions.
World powers and Iran have weeks to revive the 2015 nuclear deal after Tehran began to enrich uranium at higher levels and Iran's parliament threatened to curb the access of UN inspectors next month, the head of the global atomic watchdog said on Monday.