“We’re not going to respond to every public statement made by Iranian officials or negotiate in public. Sanctions will be suspended in a phased manner upon verification that Iran has met specific commitments under a finalized joint comprehensive plan of action," said State Department spokesman Jeff Rathke.

This comes as the Iranian Supreme Leader Ayatollah Ali Khamenei demanded that all sanction on Iran be lifted as soon as final agreement on Tehran’s nuclear program is reached. Khamenei is the most powerful figure in Iran and has the final word on all matters of state.

"I neither support nor oppose the deal. Everything is in the details, it may be that the deceptive other side wants to restrict us in the details," Khamenei said in a speech broadcast live on state television Thursday.

"All sanctions should be removed when the deal is signed. If the sanctions removal depends on other processes, then why did we start the negotiations?" he added.

This echoes remarks made by President Hassan Rouhani delivered the same day: "We will not sign any deal unless all sanctions are lifted on the same day ... We want a win-win deal for all parties involved in the nuclear talks."

The UN Security Council, the US, the EU and several other countries had imposed several rounds of sanctions against Iran due to its controversial nuclear program.

Lifting of the sanctions in exchange for a scaling-down of nuclear enrichment activities and a degree of international control over the Iranian nuclear industry is at the core of the deal. Agreeing exact terms on how quickly the sanctions will be lifted and how the program will be curtailed was a tough task for the nuclear negotiators.

The West says insists Iran fully cooperates on an IAEA investigation into past nuclear activities, the so-called possible military dimensions (PMDs).

“PMD is out of the question. It cannot be discussed,” an Iranian official said as quoted by Reuters. Khamenei also has said that “Iran’s military sites cannot be inspected under the excuse of nuclear supervision.”

But any final deal would require a vigorous monitoring framework to ensure the Iranians comply.

The French negotiating team said that reaching a final deal would be very difficult and that in any case a mechanism would have to be in place to put sanctions back in place in the event that Tehran violates it commitments.

"Subjects remain that we aren't agreed on, notably on economic sanctions, and the Supreme Leader has made statements that show there is still a lot of work to be done," French Foreign Minister Laurent Fabius told lawmakers.

Khamenei also said the tentative deal agreed earlier this month does mean a final deal will be reached by the June 30 deadline.

An interim deal was agreed last week between Iran and six world powers, the US, Russia, China, France, the UK and Germany.

The Western powers accuse Iran of trying to develop nuclear weapons. Iran denies this and says it has a right to a peaceful nuclear program. Tehran is ready to pull out of the negotiations if necessary and has said that no deal is better than a bad deal.