Ayatollah Ali Khamenei also insisted that Iran will only sign a deal if international sanctions are lifted first, which could further complicate the negotiations. The ratified bill, now binding law, calls for all sanctions to be lifted the first day of implementation.

The supreme leader has backed his negotiators amid criticism from hard-liners, but his latest remarks may narrow their room to manoeuvr ahead of a self-imposed June 30 deadline for a potentially groundbreaking deal with world powers that would curb Iran's nuclear activities in exchange for lifting sanctions.

Iran's constitutional watchdog, known as the Guardian Council, ratified legislation banning access to military sites and scientists, making it binding law, according to state TV.