Iran and the six world powers prepared on Friday for rare talks aimed at easing fears that a deepening dispute over the Islamic Republic's nuclear programme could plunge the Middle East into a new war.

Officials from Iran and the six major powers arrived in Istanbul ahead of Saturday's bid to restart stalled diplomacy following months of soaring tension and persistent speculation that Israel might attack Iranian nuclear sites.

The meeting is widely seen as a chance for the powers - the United States, France, Russia, China, Britain and Germany - and Iran to halt a downward diplomatic spiral and start to seek ways out of years of deadlock.

The West accuses Iran of seeking to develop a nuclear weapons capability and Israel has hinted at pre-emptive military strikes to prevent its arch foe from obtaining such arms.

Iran, which has come under increasingly tough Western sanctions targeting its oil exports, says its nuclear programme is peaceful and has repeatedly ruled out suspending it.

Diplomats and analysts played down any expectations of a major breakthrough in the first round of discussions, but said the meeting may pave the ground for further negotiations aimed at resolving the decade-long row.

Western officials have made clear their immediate priority is to convince Tehran to cease the higher-grade uranium enrichment it started in 2010. Iran has since sharply expanded that work, shortening the time it would need for any weapons break out.

Iran has signalled some flexibility over halting this work - refining uranium to a fissile purity of 20 percent compared with the 5 percent level required for power plants - but also suggests it is not ready to do so yet.

The talks will begin a very complex negotiation, and for several months diplomacy will take some pressure off oil prices and help keep the chance of Israeli strikes very low, said Cliff Kupchan, a Middle East analyst at the Eurasia Group.

But in the end, Kupchan said renewed diplomacy was unlikely to yield a resolution to the crisis, which has helped push global oil prices higher this year.

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Iranian state television showed footage of Iranian chief nuclear negotiator Saeed Jalili getting into a car at the airport of Turkey's biggest city.

The head of Iran's Supreme National Security Council, Saeed Jalili, arrived in Istanbul on Friday and was welcomed by local officials as well as Iran's envoy to Turkey, Bahman Hosseinpour, Iran's official IRNA news agency said.

Jalili headed a four-member Iranian delegation, state television said. An Iranian news agency later said his deputy Ali Baqeri held talks with a senior Chinese official in Istanbul on Friday and would also meet a Russian delegate.

The formal talks with the six powers and their chief representative, European Union foreign policy chief Catherine Ashton, will get underway on Saturday, but Ashton and Jalili are expected to meet over dinner on Friday evening.

The last time the two sides met, also in Istanbul in January last year, they could not even agree an agenda.

Both sides signalled in the run-up to Saturday's discussions their intent to give diplomacy a real chance.

We hope that this first round will produce a conducive environment for concrete results through a sustained process, Ashton's spokesman Michael Mann said in an email.

Iranian Foreign Minister Ali Akbar Salehi, in a rare opinion piece in a U.S. newspaper, said his country hoped that all sides would commit to comprehensive dialogue and that negotiators make genuine efforts to reestablish confidence and trust.

Defying toughening sanctions, Iran has continued to expand its uranium enrichment programme - activity which can have both civilian and military purposes - and experts say it now has enough material for four atomic bombs if processed much further.

Mark Fitzpatrick, a director of the International Institute for Strategic Studies think-tank, said getting Iran to halt 20 percent enrichment would be an interim goal to put a lid on the most troublesome aspect of Iran's nuclear programme.

A long-term deal will have to provide confidence that Iran cannot quickly produce nuclear weapons, he told Reuters, adding this would require both better monitoring of Iran's nuclear work and limits on its uranium enrichment and stockpiles.

(Additional reporting by Zahra Hosseinian, Jonathan Burch, Alexandra Hudson, Ayla Jean Yackley and Ece Toksabay; Editing by Jon Hemming)