Diplomats have gathered in a 19th century Ottoman palace on the banks of the Bosphorus to discuss one of the thorniest issues of the 21st century: Iran's nuclear program.
Iran's top nuclear negotiator, Saeed Jalili, was meeting Friday for the second time in two months with representatives of what's known as the "P5 plus 1," the five permanent members of the United Nations Security Council: the United States, France, Russia, China, and Britain plus Germany.
At issue are Western fears that Iran may be covertly trying to develop a nuclear weapon -- charges Tehran vehemently denies.
The Iranian government insists it is being bullied by its Western rivals, and prevented from being able to develop nuclear technology for civilian energy needs.
When this group of diplomats last met for negotiation in Geneva, Switzerland, in December, they succeeded in agreeing on little more than holding a second meeting in Istanbul.
That meeting took place amid simmering tensions between the United States and Iran.
At the conclusion of the Geneva talks, Jalili, the head of the Iranian delegation, gave a press conference next to a photo of an Iranian nuclear scientist who was killed by a car bomb in Tehran in November 2009. Iranian officials have accused their American and Israeli arch-rivals of assassinating two Iranian nuclear experts.
Washington formally denies such accusations. The U.S. government has led international efforts to isolate and punish Iran with economic sanctions.
"From the outset, we have had a dual track approach, diplomacy and pressure in order to have Iran comply with its international obligations," wrote Michael Hammer, spokesman for the National Security Council, in an e-mail to journalists this week.
Iranian officials bristle at the sanctions.
"Our enemies cannot harm our very strong economy by imposing sanctions," Iranian President Mahmoud Ahmadinejad said during a visit to Istanbul last month.
"The rhetoric we've seen from both Iran and the United States in the last 32 years has been extraordinary," says Iran expert Scott Peterson, author of "Let the Swords Encircle Me." "It is constant, it is always undermining and it's complete poison."
Despite this poisonous atmosphere, diplomats gathered for what sounded like a cordial dinner on the eve of the Istanbul talks.
Turkish foreign minister Ahmet Davutoglu hosted the delegations Thursday night at Istanbul's Dolmabahce Palace.
"There was one table only that everybody sat together at," Turkish foreign ministry spokesman Selcuk Unal said.
Among those at the table were Iran's Jalili, U.S. Under Secretary for Political Affairs William Burns, and the European Union's foreign policy chief Catherine Ashton, who is overseeing the negotiations.
This week's closed door meeting is expected to conclude on Saturday.