Khamenei, who enjoys the last say on all Iranian matters, was speaking for the first time on the interim nuclear deal reached between Iran and the six world powers last week in the Swiss city of Lausanne.
Speaking at a gathering of religious poets, Khamenei said he "is neither for nor against" the interim nuclear deal on curbing Iran's atomic ambitions.
The interim agreement of Lausanne provides only the framework of a possible final deal and is not an accord itself, "nothing has been done yet," he said, as a matter-of-factly.
"What has happened so far neither guarantees a deal... nor does it guarantee the content of a deal," he said. "It doesn't even guarantee the talks will go on until the end and will lead to a deal."
Khamenei however said that the punitive "sanctions should be lifted completely, on the very day of the deal".
He urged Iranian negotiators not to accept any "unconventional inspections" of Iran's nuclear facilities.
He however did express his ongoing support for the nuclear negotiations and said he is open to a compromise deal that "respects Iran's dignity and honor."
He stressed that the inspection of military facilities would not be permitted.
The spiritual leader termed as "devilish intentions" the US moves of releasing a fact sheet following the talks that outlined Washington's interpretation of the agreement.
Iran and the six world powers the five permanent UN Security Council members and Germany have set June 30 deadline to work out their disagreements.
But Khamenei said it would not be "the end of the world" if that deadline is extended.
Iran's President Hassan Rouhani also aimed high during a ceremony Thursday marking Iran's nuclear technology day, which celebrates the country's atomic achievements.
"We will not sign any agreement unless all economic sanctions are totally lifted on the first day of the implementation of the deal," Rouhani said.
Iran has repeatedly demanded the sanctions be removed immediately and permanently, while the United States prefers a more gradual phasing-out process to ensure Iranian compliance.