Iran's foreign minister is holding out hope that a "sustainable, mutually respectful" deal can be struck with world powers in talks over his country's nuclear program before the current deadline of June 30.

Mohammad Javad Zarif says an agreement with negotiators from the U.S., Russia, China, Britain, France and Germany is possible provided "people have their foot in reality, not in illusions."

But he warned that "excessive demands" would make an agreement hard to envisage, even without a deadline. Zarif spoke after talks in Athens Thursday with his Greek peer, Nikos Kotzias

The proposed deal would freeze Iran's nuclear program for a decade, in return for sanctions relief. Iran insists its nuclear program is solely for peaceful purposes, while the West fears it could allow it to build nuclear weapons.