GENEVA: US Secretary of State John Kerry joined fellow big power foreign ministers in Geneva on Friday to help clinch an interim nuclear deal with Iran and ease a decade-old standoff, with Israel warning they were making an epic mistake.

Diplomats said a breakthrough at this week’s negotiations remained uncertain and would in any case mark only the first step in a long, complex process toward a permanent resolution of Iran’s dispute with the West over its nuclear ambitions.

But they said the arrival of Kerry, British Foreign Secretary William Hague and French and German foreign ministers Laurent Fabius and Guido Westerwelle was a sign that the five powers and Germany may be closer to an agreement with Iran than ever before.

Kerry was expected to hold a trilateral meeting with European Union foreign policy chief Catherine Ashton and Iranian Foreign Minister Mohammad Javad Zarif.

A senior US State Department official said Kerry was committed to doing “anything he can” to narrow differences with the Islamic Republic. The powers aim to cap Iran’s nuclear work to prevent any advance toward a nuclear weapons capability.

The top US diplomat arrived from Tel Aviv, where he met Israeli Prime Minister Benjamin Netanyahu.

Netanyahu warned Kerry and his European counterparts that Iran would be getting “the deal of the century” if they carried out proposals to grant Tehran limited, temporary relief from sanctions in exchange for a partial suspension of, and pledge not to expand, its enrichment of uranium for nuclear fuel.