UNITED NATIONS -- The U.S. and its international partners emerged from a meeting with Iran declaring that a "window of opportunity has opened" to peacefully settle their nuclear standoff. But diplomats asked Tehran to come back with a detailed plan of action to reassure the world it is not trying to build an atomic bomb.
The upbeat, if guarded, tone after the meeting of Iran, the five permanent members of the U.N. Security Council and Germany was seen as a significant step forward after months of stalled talks. It was capped by an unexpected one-on-one meeting between U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif, who shook hands and at one point sat side-by-side in the group talks on Thursday.
It was the highest-level direct contact between the United States and Iran in six years.
In another sign of building momentum, both sides agreed to fast-track negotiations and hold a substantive round of talks on Oct. 15-16 in Geneva. Iran, hoping to get relief from punishing international sanctions as fast as possible, said it hoped a resolution could be reached within a year.
"We agreed to jump-start the process so that we could move forward with a view to agreeing first on the parameters of the end game ... and move toward finalizing it hopefully within a year's time," Zarif said after the talks. "I thought I was too ambitious, bordering on naivete. But I saw that some of my colleagues were even more ambitious and wanted to do it faster."
European Union foreign policy chief Catherine Ashton also said the parties had agreed to "go forward with an ambitious timeframe."
Kerry said he was struck by the "very different tone" from Iran. But along with his European colleagues, he stressed that a single meeting was not enough to assuage international concerns that Iran is seeking to develop nuclear weapons under cover of a civilian atomic energy program.
"Needless to say, one meeting and a change in tone, that was welcome, does not answer those questions," Kerry told reporters. "All of us were pleased that the foreign minister came today and that he did put some possibilities on the table."
He said they agreed to try to find concrete ways to answer the questions that people have about Iran's nuclear activities.
As the group meeting was ending, Kerry leaned over and asked Zarif: "Shall we talk for a few minutes."
A senior U.S. official said that in the one-on-one meeting, aides from both sides chatted in a marked departure from past encounters, when the Iranians were tight-lipped. It was one of the signs of a new attitude, said the official who spoke on condition of anonymity because he was not authorized to talk to the media.
The official also said Zarif presented a number of ideas -- many that had come up before - but they were not particularly detailed. The Americans asked Zarif to come back at the Geneva round or even earlier with some more detailed proposals.
Zarif said the end result would have to include "a total lifting" of the international sanctions that have ravaged Iran's economy.
"We hope ... to make sure (there is) no concern that Iran's program is anything but peaceful," he said. "Now we have to see whether we can match our positive words with serious deeds so we can move forward."
British Foreign Secretary William Hague said there had been a "big improvement in the tone and spirit" from Iran compared with the previous government under Mahmoud Ahmadinejad.
German Foreign Minister Guido Westerwelle said the meeting had taken place in a "completely different tone, atmosphere and spirit" than what the group was used to and that a "window of opportunity has opened" for a peaceful resolution of the situation. He too insisted that Iran's words would have to be matched by actions.
"Words are not enough," he said. "Actions and tangible results are what counts. The devil is in the detail, so it is now important that we have substantial and serious negotiations very soon."
Iranian President Hassan Rouhani and Zarif, both in New York this week to attend the U.N. General Assembly, have said they are anxious to clinch an agreement quickly that could bring relief from sanctions. The sanctions have slashed Iran's vital oil exports by more than half, restricted its international bank transfers, devalued its currency and sent inflation surging.
Encouraged by signs that Rouhani will adopt a more moderate stance than Ahmadinejad, but skeptical that the country's all-powerful supreme leader will allow a change in course, President Barack Obama has directed Kerry to lead a new outreach and explore possibilities for resolving the long-standing dispute.
Rouhani has come across as a more moderate face of the hard-line clerical regime in Tehran and his pronouncements at the U.N. have raised guarded hopes that progress might be possible. But they have also served as a reminder that the path to that progress will not be quick or easy.
He has steadfastly maintained that any nuclear agreement must recognize Iran's right under international treaties to continue enriching uranium.
The U.S. and its allies have long demanded a halt to enrichment, fearing Tehran could secretly build nuclear warheads. They have imposed sanctions over Iran's refusal to halt enrichment. Uranium enriched to low levels can be used as fuel for nuclear energy but at higher levels, it can be used to make a nuclear weapon.
Rouhani also insisted 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.
Those conditions underscored that there is still a large chasm to be bridged in negotiations.
Rouhani has made a series of appearances and speeches since arriving in New York and has held bilateral negotiations with France, Turkey and Japan among others.
On Thursday, he called for worldwide disarmament of nuclear weapons as "our highest priority."
Speaking at the first-ever meeting of a U.N. forum on nuclear disarmament on behalf of the Non-Aligned Movement, an organization of mostly developing countries, Rouhani repeated the organization's long-standing demand that Israel join the international treaty banning the spread of nuclear weapons.
Israel, which has repeatedly accused Iran of aspiring to build a nuclear bomb, is the only Mideast state that has not signed the landmark 1979 Non-Proliferation Treaty.
Rouhani appears to be trying to tone down Ahmadinejad's caustic rhetoric against Israel -- a point of friction in relations with the U.S. But Israel is not biting and reacted angrily to his latest remarks.
"Iran's new president is playing an old and familiar game by trying to deflect attention from Iran's nuclear weapons program," said Intelligence and International Affairs Minister Yuval Steinitz. "The problem of the NPT in the Middle East is not with those countries which have not signed the NPT, but countries like Iran, Iraq, Libya and Syria which have signed the treaty and brazenly violated it," he added.
"Unlike Iran, Israel has never threatened the destruction of another country," he said.
Iran watchers say Rouhani may have limited time to reach a settlement -- possibly a year or less -- before Khamenei decides negotiations are fruitless.
At a separate forum across the city, Rouhani said his government is ready to work with the world powers and others to ensure full transparency under international law regarding the nuclear program.
"My government is prepared to leave no stone unturned in seeking for a mutually acceptable solution," he said.