Three o’clock in the Geneva morning. Perhaps they had to pinch themselves to make sure this wasn’t a dream. After all, for thirty odd years this would have made an unbelievable scene.

America and Iran putting aside decades of animosity as John Kerry and Mohammad Javad Zarif smiled and shook hands on a deal that offers a new start for the Middle East.

No wonder Barack Obama was so quick to herald this agreement - it is the big foreign policy triumph of his presidency. And if it works, he can claim to have used diplomacy to solve a crisis that has threatened to plunge the region into war.

Warning: John Ray's report contains flash photography:

Watch: Barack Obama says nuclear deal is an important first step

But already it puts America at serious odds with its long-term friends Israel and Saudi Arabia – who both have good reason to fear a nuclear-bolstered Tehran’s ability to dominate the Gulf and beyond.

The really optimistic might also hope this is a preface to further co-operation between Washington and Iran over Syria.

The Israeli Prime Minister's denunciation of the Geneva deal was predictable but should not be simply dismissed. Benjamin Netanyahu likens the risk of an atomic-armed Islamic Republic to a second Holocaust. The anti-Zionist rhetoric that comes out of Tehran doesn’t help.

Read: Israeli PM says Iran deal has made world 'much more dangerous'

Israel retains the right to strike militarily, but in reality its options have just been severely limited.

More likely they will push - alongside, more discretely, the Gulf nations - for a tough line in the six months of hard negotiations that now follow this interim agreement.

It is too early to call the breakthrough in Geneva truly historic. And there are many, from the hardliners in Jerusalem and Tehran, to the hawks of Washington and beyond, who are willing it to fail.

Read: What Iran gets in nuclear programme deal