In a historic move, US Secretary of State John Kerry and his Iranian counterpart met one-on-one Thursday, a thawing of ties that raised hopes of a breakthrough in the foes' nuclear stand-off.

The brief encounter, one of the highest-level between the two foes since Iran's 1979 Revolution, came as world powers hailed a fresh impetus in nuclear talks with Iran, which have made little progress for years.

Kerry said he and his counterparts from the great power contact group known as the P5+1 praised Mohammad Javad Zarif's presentation "which was very different in tone, and very different in the vision that he held out with respect to the possibilities in the future."

The nuclear talks will now resume on October 15 and 16, boosting hopes that Iran will bring tangible proposals to the table on how to move forward as the west seeks to rein in its nuclear program.

The top US diplomat said he had met with Zarif, who took up his post in August, "on a side meeting in which we took a moment to explore a little further the possibilities of how to proceed."

It was an extraordinary contact between the two countries which have had no diplomatic relations since 1980, when Iranian students stormed the US embassy in Tehran and embarked on a prolonged hostage-taking.

Kerry said the two men had agreed to try to find a "concrete" way to "answer the questions that people have about Iran's nuclear program."

Zarif, whose country still refers to the United States as the "Great Satan," also hailed his talks with the P5+1 as "very substantive."

He and Kerry had stressed "the need to continue these discussions to give it the political impetus that it requires and to hopefully to reach a conclusion within a reasonable time," he said.

Chaired by EU foreign policy chief Catherine Ashton, the meeting brought together the foreign ministers of the five permanent members of the UN Security Council, Britain, China, France, Russia and the United States plus Germany.

Smiling broadly, Zarif was seen sitting at the head of the table next to Ashton looking down on a Security Council conference room, with Kerry to the right on an abutting table.

But western powers have approached with caution the overtures made by the new Iranian leadership which took power in August.

And Kerry said "needless to say one meeting and a change in tone, which was welcome, doesn't answer" all the questions on Iran's nuclear program.

"There's a lot of work to be done," he stressed.

It is the first time that Iranian and American ministers have sat together at the talks, aimed at reining in the Islamic republic's nuclear program, which western nations believe is a covert grab for an atomic bomb.

But new Iranian President Hassan Rouhani said his country was committed to negotiate in "good faith."

"We are fully prepared to seriously engage in the process toward a negotiated and mutually agreeable settlement and do so in good faith and with a business-like mind," Rouhani told a think tank forum in New York.

Rouhani has said he believed a deal could be struck with the international community within three to six months.

And Ashton hailed what she called an ambitious timeframe as she confirmed that the next round of talks would be held in Geneva next month.

"It was a substantial meeting, good atmosphere, energetic," she told reporters after the talks.

Like Zarif she said she was "very ambitious about what we can do, but we have to be practical about translating that ambition into what does that mean for the effective work we do on the ground."

Earlier Rouhani, speaking as current leader of the Non-Aligned Movement at a conference on disarmament, highlighted the failure of attempts to organize a Middle East nuclear free zone.

"Israel, the only non-party to the Non-Proliferation Treaty in this region, should join thereto without any further delay," Rouhani told the meeting.

The P5+1 made a new offer to Iran earlier this year, before Rouhani's election, on how to overcome the current stalemate in the nuclear dossier.

It is believed to have offered an easing of the international sanctions which have crippled the Iranian economy, in return for a slow down in Iran's uranium enrichment program.

Ashton said it was now up to Iran to either respond to the offer or come forward with new proposals, adding that they had asked Zarif to give them as "much notice as possible" before the Geneva talks.

The United States had sought a meeting between President Barack Obama and Rouhani on the sidelines of this week's UN assembly. But Iran said it was too complex to organize.