Iran's Foreign Minister Mohammad Javad Zarif
Iran's Foreign Minister Mohammad Javad ZarifReuters

Iranian Foreign Minister Mohammad Javad Zarif said Sunday that clinching a final nuclear deal with world powers is still "possible" despite a tough round of talks this week, AFP reports.

"Agreement is possible. But illusions need to go. Opportunity shouldn't be missed again like in 2005," Zarif wrpote on Twitter, referring to Iran's long-stalled dispute with world powers over its suspect nuclear program.

Iran and six world powers ended a fourth round of nuclear talks in Vienna on Friday with "no tangible progress".

Britain, China, France, Russia, the United States and Germany -- known as the P5+1 group -- want Iran to radically scale back its nuclear activities, making any dash for an atomic bomb virtually impossible and easily detectable.

The parties want to clinch a deal by July 20, when a November interim deal expires, under which Iran froze certain activities in return for some relief from crippling Western sanctions.

In return for further concessions, the Islamic Republic, which denies seeking an atomic weapon, wants the lifting of all UN and Western sanctions, which have caused major damage to its economy.

Iran has not convinced everyone with its professed possession of a peaceful nuclear program, a doubt that was raised on Sunday when Iran's Supreme Leader, Ayatollah Ali Khamenei, said Western expectations that Iran limit its missile program were "stupid and idiotic."

Similarly in January, Khamenei stated that negotiations with the U.S. were a tactic to gain time.

Israel has warned that the interim deal is dangerous and allows Iran to continue its nuclear program while getting sanctions relief.

Prime Minister Binyamin Netanyahu repeated those warnings on Friday, telling visiting U.S. Defense Secretary Chuck Hagel that world powers must deny Iran any possibility of developing a nuclear weapon as the search for a deal intensifies.

"I think that, while the talks with Iran are going on, there is one thing that must guide the international community and that is not to let the ayatollahs win," Netanyahu's office quoted him as saying at the beginning of their meeting in Jerusalem.

"We must not allow Iran, the foremost terrorist state of our time, to develop the ability to develop a nuclear weapon," Netanyahu said.