A new effort to break the deadlock over Iran's nuclear ambitions is set to begin after 10 hours of talks between Tehran and the world's leading powers ended with rare words of mutual praise.
The first formal negotiations between Iran and a six-nation contact group, including America and Britain, for over a year ended with agreement that diplomats will prepare concrete proposals for resolving the impasse.
Saeed Jalili, secretary of Iran's Supreme National Security Council, took the unusual step of commending his adversaries at the conclusion of the session in Istanbul.
"Today, we saw a positive approach and we consider it a step forward," he said. "For the Iranian people, the language of pressure doesn't work, but the language of co-operation could be fruitful. Today, we witnessed such an approach."
Mr Jalili, an often irascible hardliner, adopted a very different tone during his last encounter with the "P5 plus 1", consisting of the five permanent members of the Security Council – America, Britain, Russia, France and China – along with Germany.
On that occasion last January, he declined to even talk about Iran's nuclear programme unless all sanctions were lifted. "Outside the room, he's very charming and he enjoys all the photo opportunities. Inside the room, he's a completely different character. I wouldn't trust him with my children," said an ex-official who observed those talks.
"He goes off on long-winded, the West is evil, anti-Western rhetoric. He could do a whole intervention in 10 minutes of monotone."
This time, however, diplomats noted Mr Jalili's wholly different, "calm and constructive" approach. One said: "We had a whole day talking about the nuclear issue and only the nuclear issue."
Baroness Ashton, the European Union's high representative for foreign policy, who chairs the "P5 plus 1", had a three-hour dinner with Mr Jalili on Friday night. After the talks, Lady Ashton described them as "constructive and useful", adding: "We want now to move to a sustained process of serious dialogue, where we can take urgent practical steps to build confidence and lead on to compliance by Iran with all its international obligations."
The two sides will meet again in Baghdad on May 23. Before then, two senior negotiators will try to hammer out concrete proposals. Helga Schmid, who serves as Lady Ashton's deputy, will represent the "P5 plus 1", while Ali Baqeri, a senior Iranian diplomat, will speak for Tehran.
But Mr Jalili brought no specific proposals to Istanbul and the gap between the two sides remains as wide as ever. "Our delight is well within bounds: it's beer not champagne," said one diplomat.
Iran insists on its right to continue enriching uranium, a sensitive process that could be used to make the material for a nuclear weapon. America, Britain and the other "P5 plus 1" countries, meanwhile, want Iran to obey six United Nations resolutions and stop enrichment.
Moreover, neither side trusts the other. Mr Jalili's tone was conciliatory, but diplomats noted that he did not bring any concrete proposals to Istanbul. Nor did he accept the offer of a one-on-one meeting with his American counterpart, Wendy Sherman.
Instead, Mr Jalili repeated Iran's insistence on enriching uranium, saying this was a "right" under the nuclear non-proliferation treaty, adding: "Any right which is included in the NPT should be respected. Enrichment of uranium is one of those rights that every member state should benefit from for peaceful purposes."
Mr Jalili spoke in front of a banner, hastily raised by his officials, reading: "Nuclear Energy for All, Nuclear Weapons for None." This showed a gallery of photographs of five Iranian scientists, all of them killed by bomb attacks in Tehran allegedly masterminded by Israeli intelligence.
Diplomats are alert to the danger that Iran might try to use this new diplomatic effort to buy time for its nuclear programme to progress. They are deeply worried that Israel could lose patience and launch a unilateral strike to destroy Iran's nuclear facilities.
These dangers must impose a time limit on the new effort to settle the issue. "We can't be messing around like this at the end of the year," said one diplomat.