US has not maintained diplomatic relations with Iran since 1980
Iran's new government took its diplomatic charm offensive to the United Nations on Monday and agreed to new talks on its nuclear program with top diplomats from six world powers, including US Secretary of State John Kerry.
The meeting bringing the top US diplomat and new Iranian Foreign Minister Mohammad Javad Zarif around the same conference table will be highly unusual given the United States has not maintained diplomatic relations with Iran since 1980.
The announcement of the talks planned for this week during the UN General Assembly in New York, raised hopes that the annual summit of world leaders could bring a thaw in relations between arch-enemies Iran and the United States.
US officials have also said a meeting is possible this week between President Barack Obama and Iran's new centrist president, Hassan Rouhani, who has shown an apparent desire to take a more conciliatory approach towards the West since taking office last month.
If that meeting were to happen, it would be the first between US and Iranian government heads since before the 1979 Islamic revolution that toppled the US-backed Shah, and could help ease tensions in the Middle East that have been worsening given the crisis in Syria.
Iran is a key ally of Syrian President Bashar Al Assad, a US foe whose country has been torn by civil war since 2011.
UN Secretary-General Ban Ki-moon has invited world leaders attending the General Assembly, including Rouhani and Obama, to attend an annual luncheon at the United Nations on Tuesday. That would be one possibility for the two men to meet briefly. Obama skipped last year's UN luncheon, but the White House said he would attend this year.
Obama and Rouhani will both address the assembly on Tuesday.
EU foreign policy chief Catherine Ashton said after talks with Zarif that he would join her and his counterparts from the five permanent members of the UN Security Council and Germany at a meeting that has been scheduled for Thursday to discuss Iran's nuclear program, which is at the heart of tensions between Tehran and the West.
The West believes Iran has been trying to develop nuclear weapons and is determined to stop this, imposing tough economic sanctions. Iran says it is not trying to produce a bomb but has insisted on its right to enrich uranium for the purpose of peaceful energy production.
The EU, led by Ashton, has chaired the talks between Iran and the so-called P5+1 - Britain, China, France, Russia and the United States, as well as Germany - which have made little headway in spite of years of negotiations.
Ashton said the meeting in New York would be "short discussions," and added that she would represent the P5+1 in a meeting with Zarif in Geneva in October.
The last time a US secretary of state and an Iranian foreign minister spoke face-to-face appears to have been more than six years ago.
In May 2007, then-US Secretary of State Condoleezza Rice made clear she was open to talking to her Iranian counterpart, Manouchehr Mottaki, at an international conference in Egypt, but the encounter amounted to pleasantries over ice cream.
State Department spokeswoman Jen Psaki said Washington was ready to work with Rouhani if his government engaged seriously in efforts to resolve the nuclear issue.
A senior State Department official said Iran's meetings this week with European officials and ministers would show whether Iran was coming with concrete new proposals "and whether this charm offensive actually has substance."
Ashton said she had "a good and constructive discussion" in what was her first face-to-face meeting with Zarif.
Speaking after his talks with Zarif, British Foreign Secretary William Hague welcomed Iran's statements that it wants to improve relations with the West and ease concerns about its nuclear program, but he said words alone would not be enough.
"The time is now right for those statements to be matched by concrete steps by Iran to address the international community's concerns about Iran's intentions and if such steps are taken, then I believe a more constructive relationship can be created between us," Hague told reporters.
Hague said some such concrete steps had been taken with the release of some political prisoners.
"Of course we urge them down that path and hope it will be possible to take steps across a whole range of issues. If it is, we are willing to reciprocate in many ways."
Iranian media reported on Monday that authorities in Iran have pardoned 80 prisoners ahead of Rouhani's visit to the United Nations. In a tentative sign that hardline policies are starting to soften following Rouhani's inauguration last month, authorities freed prominent human rights lawyer Nasrin Sotoudeh and at least 10 other prisoners last week.
Asked about the possibility of a relaxation of sanctions on Iran - the desire for which some analysts see as the reason for the more conciliatory approach from the Iranians - Ashton praised Zarif's "energy and determination to try and move forward in our talks."
But she said they had not gone into details of the nuclear issue, including the UN Security Council's demand for Iran to suspend its uranium enrichment.
Zarif wrote on Facebook that his meeting with Ashton was "positive." He said he explained how it would be possible to "reach a solution based on the rights of the people of Iran and the removal of sanctions."
Speaking before leaving for New York, Rouhani said he would use his visit to the United Nations to present the "true face of Iran" and to pursue talks and cooperation with the West to end the nuclear dispute.
"Unfortunately in recent years the face of Iran, a great and civilized nation, has been presented in another way," he said, according to comments on his official website.
"I and my colleagues will take the opportunity to present the true face of Iran as a cultured and peace-loving country."
Rouhani, a former nuclear negotiator under reformist former President Mohammad Khatami, did not make clear who he blames for any distortion of Iran's image. But the comments suggested he was intent on distancing himself from the outspoken approach to the West adopted by predecessor Mahmoud Ahmadinejad.
Rouhani, however, also targeted the West for the suffering caused by its sanctions. He has vowed to improve Iran's ailing economy, which has suffered deeply from the measures.
Last week, the new president's tone was endorsed by Iran's most powerful figure, Ayatollah Ali Khamenei, who spoke of "heroic flexibility," suggesting a new willingness to engage in diplomacy with Iran's adversaries.
Israel, Washington's closest Middle East ally and thought to be the region's only nuclear-armed power, is suspicious of Rouhani's overtures and worries that some Western states may be too eager to relax sanctions without concrete steps by Tehran.
French Foreign Minister Laurent Fabius took a similar line to Britain's Hague ahead of a meeting between French President Francois Hollande and Iran's president on Tuesday, the first between leaders of the two nations since 2005.
"We have taken note of the positive statements of the new president Rouhani and his government," Fabius told reporters.
"These meetings will be the occasion to assess the reality of the words being used. Rouhani's first measures and speeches have shown a certain evolution and it's not the same tone as his predecessor ... all that now has to be put under the microscope of reality."
In Washington, four senior US senators - two Democrats and two Republicans - urged Obama to keep a tough stance on Iran.
Democrat Robert Menendez and Republican Lindsey Graham urged Obama to use his General Assembly speech to restate the US goal of not permitting Iran to develop nuclear weapons. In addition, Democrat Charles Schumer and Republican John McCain urged Obama not to let up on sanctions on Iran.