Foreign ministers from the five permanent members of the UN Security Council and Germany will meet with Iran's top diplomat on Thursday to test the Islamic Republic's apparent willingness to reach a deal to resolve international concerns about its nuclear program after years of defiance.
The meeting on the sidelines of the annual United Nations General Assembly is aimed at paving the way for the first round of substantive negotiations on the nuclear issue since April, probably next month. It will also mark the highest-level, direct contact between the United States and Iran in six years as Secretary of State John Kerry comes face-to-face with Iranian Foreign Minister Javad Zarif.
The United States, Britain, France, Russia, China and Germany will participate with European Union foreign policy chief Catherine Ashton serving as host of the meeting.
Encouraged by signs that new Iranian President Hasan Rouhani will adopt a more moderate stance than his hard-line predecessor but skeptical that the country's supreme leader will allow a change in course, President Barack Obama directed Kerry to lead a new outreach to explore possibilities for resolving the long-standing dispute.
However, Obama and other US officials have said Iran must prove its commitment with actions, not just words.
Rouhani is in New York this week, making his debut on the world stage with an address to the General Assembly and a series of other speeches, news conferences and bilateral meetings.
During his visit, Iran has shown new urgency in reviving the stalled negotiations, seeking to ease crippling international sanctions as quickly as possible. Rouhani said Wednesday that "we have nothing to hide" and Zarif said he hoped his counterparts "have the same political will as we do to start serious negotiations with a view to reaching an agreement within the shortest span of time."
The West suspects Iran is trying to build a nuclear weapon and has imposed crippling sanctions on Tehran that have slashed its vital oil exports and severely restricted its international bank transfers. Inflation has surged and the value of the local currency has plunged.
Tehran has repeatedly denied that its nuclear program is for anything other than peaceful purposes.
But since his June election, Rouhani has made clear he is seeking relief from the sanctions and has welcomed a new start in nuclear negotiations in hopes this could ease the economic pressure. He has said he has the full support of Iranian Supreme Leader Ayatollah Ali Khamenei, who has the final word on all important matters of state including the nuclear question.
"If there is political will on the other side, which we think there is, we are ready to talk," Rouhani told editors Wednesday in New York. "We believe the nuclear issue will be solved by negotiation."
In his speech to world leaders at the UN on Tuesday, Rouhani repeated Iran's long-standing demand that any nuclear agreement must recognize its right under international treaties to continue enriching uranium. The US and its allies have long demanded a halt to enrichment, fearing Tehran could secretly build nuclear warheads.
Uranium enriched to low levels can be used as fuel for nuclear energy but at higher levels of enrichment, it could be used to build a nuclear weapon.
Rouhani also insisted in his speech that any deal be contingent on all other nations declaring their nuclear programs too are solely for peaceful purposes - alluding to the U.S. and Israel.
Iran watchers say Rouhani may have limited time to reach a settlement - possibly a year or less - before Khamenei decides negotiations are fruitless. That may explain Zarif's call to reach a deal in the short time span.
"He is not negotiating for the sake of negotiating and dragging it out," Haleh Esfandiari, director of the Mideast program at the Wilson Center think-tank in Washington, said of Rouhani.
"His reputation, and the country's reputation, is at stake. This is an issue they are willing to work on, and move to take concrete steps to serious negotiations."
Rouhani in New York has come across as a more moderate face of the hard-line clerical regime in Tehran. In particular, he appears to be trying to tone down the caustic rhetoric of his predecessor, Mahmoud Ahmadinejad, with regard to Israel - one of the points of friction in relations with the West.
Still his speech to the UN was peppered with Iran's traditional digs at America and the West - a reminder that a diplomatic warming will not come quickly or easily.
Rouhani condemned "the Nazi massacre against Jews, Christians and others" in his remarks to editors on Wednesday.
"There is no way to ignore Nazi crimes against Jews," he said. But he added "it is important that those victimized not seek compensation by victimizing other groups" - a pointed reference to what he has described as Israel's occupation and subjugation of Palestinians.
Citing the Quran, or Muslim holy book, Rouhani said that if any innocent person is killed, it is as if all of mankind has been killed."
Ahmadinejad, in contrast, once called the Holocaust a "myth" and later said more research was needed to determine whether it had really happened.
Israel's UN delegation walked out of Rouhani's speech Tuesday in protest. But in a text message statement sent to reporters on Wednesday, Finance Minister Yair Lapid said Prime Minister Benjamin Netanyahu's instruction to Israeli delegates to walk out was a "mistake." He said it created the impression that Israel was not interested in encouraging a peaceful solution to Iran's suspect nuclear program.
Rouhani said Iran must be careful in starting a new relationship with the US after three decades of frozen ties, adding that his first goal is to reduce the distrust. He noted that there are radical voices in America and radical voices in Iran who would not like to see that happen, but said that the voices of moderation need to be strengthened and supported.
"The more two countries are apart, the more suspicions, fears and miscalculations creep in," he said in remarks that were initially supposed to be off the record. However, in response to requests from journalists, Rouhani agreed some of his remarks could be quoted.
He said he has no problem shaking hands with President Barack Obama.
But he said he thought the first meeting between leaders of their two countries in more than three decades needed to be handled very carefully.
There had been heated speculation that the two might meet at the UN on Tuesday and even exchange handshakes and pleasantries.
But that did not happen.
The White House said Obama remains open to the possibility of an informal encounter with Rouhani at a future date.