Iran's supreme leader Ayatollah Ali Khamenei on Wednesday ruled out allowing nuclear inspectors to visit military sites or to question scientists, state media reported.
"We have already said that we will not allow any inspections of military sites by foreigners," the official IRNA news agency quoted him as saying.
"They also say that we must allow interviews with nuclear scientists. This is interrogation. I will not allow foreigners to come and talk to scientists who have advanced the science to this level," Khamenei said.
The United States as well as Britain, China, France, Russia and Germany are in the midst of negotiations with Tehran to finalise a deal by June 30 that would prevent Iran from developing nuclear weapons, in exchange for an easing of crippling economic sanctions.
If fully implemented, a deal will see Iran dramatically scale back its nuclear activities and submit those that remain to what US President Barack Obama has described as the "most robust and intrusive inspections and transparency regime ever negotiated".
Iran has long asserted its nuclear programme is for peaceful energy purposes, and that international concern about it seeking a nuclear bomb is misplaced.