IRAN and six world powers began rare talks yesterday to try to halt a downward diplomatic spiral over Tehran's nuclear programme and ease fears of a new Middle East war.

Western diplomats hope the talks, in Istanbul, the first between Iran and the six powers – United States, France, Russia, China, Germany and Britain – in 15 months will show a readiness from Tehran to start to discuss nuclear issues substantively.

That, they say, would mark a big change in Iran's attitude from the last meeting when it refused even to talk about its nuclear programme and could be enough for scheduling a second round of talks next month, possibly in Baghdad.

Such an outcome could, at least for the time being, dampen speculation that Israel might launch military strikes on Iranian atomic sites.

The morning round of talks was "completely different" from the previous meeting 15 months ago and Iranian chief nuclear negotiator Saeed Jalili had not stated the kind of preconditions that he did in the last meeting in early 2011, a diplomat said.

"He seems to have come with an objective to get into a process which is a serious process," said the envoy, who spoke on condition of anonymity. "I would say it has been a useful morning's work."

Both sides say they are ready at the meeting to work towards resolving the deepening dispute over the nuclear programme, which the West suspects is geared towards achieving a nuclear arms capability, but which Iran says has purely peaceful purposes.

"What we are here to do is to find ways in which we can build confidence between us and ways in which we can demonstrate that Iran is moving away from a nuclear weapons programme," said European Union foreign policy chief Catherine Ashton who is also the main representative of the United States, France, Russia, China, Germany and Britain at the talks.

Iran says it will propose "new initiatives" in Istanbul, but it is unclear whether this means it is now prepared to discuss curbs to its uranium enrichment programme.

The West accuses Iran of seeking to develop a nuclear weapons capability. Israel – believed to be the only Middle East state with an atomic arsenal – sees Iran's atomic plans as a threat to its existence. Iran has threatened to retaliate for any attack by closing a major oil shipping route.

Iran, one of the world's largest oil producers, says its nuclear programme is a peaceful attempt to generate electricity and medical isotopes for cancer patients.