Iran's supreme leader has hardened his stance on the nuclear negotiations with world powers, with the deadline for a comprehensive agreement only days away, BBC News reported.

In a speech on Tuesday, June 24 night, Ayatollah Ali Khamenei insisted Iran would only dismantle its nuclear infrastructure if economic sanctions were lifted first.

He also ruled out a freeze on research and development for 10 years, as well as inspections of military sites.

The demands appear to undercut a framework deal announced in April.

They could also limit the ability of Iran's negotiating team to make key concessions as the self-imposed 30 June deadline approaches.

As supreme leader, Ayatollah Khamenei has final say on all state matters.

The so-called P5+1 - the US, UK, France, China and Russia plus Germany - want Iran to scale back its sensitive nuclear activities permanently to ensure that it cannot build a nuclear weapon. Iran insists its nuclear work is peaceful.