Zarif says an agreement with negotiators from the US, 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 on Thursday with his Greek peer, Nikos Kotzias.

The proposed deal would freeze Iran's nuclear program fora 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.

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