Iran has committed to reaching a settlement over its controversial nuclear programme within a year after talks hailed as a breakthrough by the US and its European allies.
Iranian foreign minister Mohammad Javad Zarif met with members of the 'P5+1' group - US Secretary of State John Kerry, British foreign secretary William Hague and top diplomats from France, Germany, China and Russia.
The parties agreed to hold a second substantive round of talks on 15 October in Geneva.
"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 finalising it hopefully within a year's time," Zarif said.
"I thought I was too ambitious, bordering on naiveté. But I saw that some of my colleagues were even more ambitious and wanted to do it faster."
Hague said there had been a "big improvement in the tone and spirit" of Iran since Mahmoud Ahmadinejad was replaced as president by the more moderate Hassan Rohani.
However Kerry stressed that a single meeting was not enough to assuage international concerns that Iran is seeking to develop nuclear weapons.
Tehran has repeatedly denied that its nuclear programme is designed for anything other than peaceful purposes, but the US, Israel and the EU have long suspected Iran is trying to develop a nuclear weapon.
"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."
Kerry's sentiments were echoed by German foreign minister Guido Westerwelle, who said that "words are not enough."
Westerwelle continued by saying that "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."
The meeting came after Rohani said he was willing to reset diplomatic relations with the West, starting with the nuclear issue, during a visit to New York to attend the UN General Assembly.
'Rohani is smiling his way to the bomb'
A conciliatory Rohani gave several interviews to major US publications in a charm offensive, which analysts believe is designed to ease the economic sanctions imposed on Iran.
Zarif said the end result of nuclear talks would have to include "a total lifting" of sanctions.
Israel remained suspicious of Tehran intentions.Yuval Steinitz, the head of the Jerusalem's delegation to the UN, said that Rohani "is playing an old and familiar game by trying to deflect attention from Iran's nuclear weapons programme.
"[He is trying] to smile his way to the bomb."