As senior envoys from Iran and six world powers worked on a nuclear deal this week in Geneva's InterContinental Hotel, the lobby was bustling with scenes that would have been unimaginable only a few months ago. Late one night, journalists from Tehran abandoned political inhibitions and chatted with a Persian-speaking US diplomat by the fireside. Nearby, a member of the Islamic Republic's delegation talked to US reporters who were nursing drinks from the bar.
The relaxed atmosphere mirrored the thawing relations between Washington and Tehran, which in turn could lead to a wider easing of tensions across the Middle East.
The initial nuclear deal reached this weekend between Iran and six world powers - Britain, China, France, Russia, the United States and Germany - may prove to be the pivotal moment when Tehran returned to the diplomatic fold after years of being sidelined by Western capitals.
"We thought that that was an unnecessary issue," Iran's Foreign Minister Mohammad Javad Zarif said Sunday, referring to the decade-long nuclear stand-off.
"It prevented the addressing of more important issues that are of paramount importance to us, to the region and to the world in general," he added.
"A quiet arrangement with the US on regional politics is becoming ever more important from Tehran's viewpoint - and this is only possible by solving the nuclear conflict," Iran expert Walter Posch at the German Institute for International and Security Affairs in Berlin wrote recently.
Iran's foreign policy changed as soon as Hassan Rowhani succeeded the hard-liner Mahmoud Ahmadinejad as Iranian president in August.
Rowhani has vowed to get the sanctions lifted that have led to inflation and to an embargo of Iranian oil - a major source of government revenue.
He held the first telephone conversation between a US and Iranian president since the 1979 Islamic revolution when he talked with Barack Obama in September, and he has also taken steps to mend ties with Britain.
At the same time, Rowhani's new administration quietly halted any expansion of nuclear facilities starting in August, even before the three rounds of Geneva nuclear talks started.
Meanwhile, the United States and other powers made a major concession of their own on the issue at the centre of the 10-year-old dispute: They did not object when International Atomic Energy Agency (IAEA) and Iran agreed this month to postpone an investigation into alleged nuclear weapons research and development projects.
This silent consent signalled that the six powers wanted to focus on Iran's present nuclear activities, rather than past weapons projects, even though their own intelligence services had collected evidence pointing to such work.
Under the deal announced Sunday, Iran accepts curbs on its uranium enrichment programme and on its efforts to build a plutonium-producing reactor at Arak for a period of six months.
In return, the six powers suspend some of their sanctions, on the condition that Tehran implements its side of the deal.
Diplomats have described this period as a "breathing space," allowing both sides to reach an final agreement that is to involve further nuclear concessions and the lifting of all sanctions.
Yet despite the strides made, high hurdles remain.
Rowhani's conservative and Islamist political rivals would like to see his diplomatic efforts fail, because they do not want the moderate president and his camp to emerge as the heroes who ended Iran's international isolation and economic crisis - a development that would weaken the position of the religious hard-liners.
In Washington, Obama faces the risk that senators vote on new sanctions targeting Iran before the end of the year, a step that could derail the Geneva deal.
Key senators have warned that now is not the time to let up pressure on Tehran and have expressed fear that easing sanctions would backfire.
Meanwhile, Israeli leaders indicated that it would not shy away from using military means if its regional enemy Iran were found to build a nuclear weapon, despite the agreement.
"It is important for the world to know: Israel will not be committed to a deal that risks its existence," Economy Minister Naftali Bennett said, according to the news portal Ynet.
However, US Secretary of State John Kerry insisted Sunday that the initial deal and the comprehensive agreement to follow would prevent Tehran from acquiring such arms.
"That will make the world safer," he said in Geneva.